First published online September 16, 2002; 10.1105/tpc.004960
The Plant Cell, Vol. 14, 2339-2351,
October 2002, Copyright © 2002,
American Society of Plant Biologists
Auxin-Mediated Cell Cycle Activation during Early Lateral Root Initiation
Kristiina Himanen,
Elodie Boucheron1,
Steffen Vanneste,
Janice de Almeida Engler,
Dirk Inzé2 and
Tom Beeckman
Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
2 To whom correspondence should be addressed. E-mail dirk.inze{at}gengenp.rug.ac.be; fax 32-9-2645349
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Abstract
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Lateral root formation can be divided into two major phases: pericycle activation and meristem establishment. In Arabidopsis, the first lateral root initiation event is spatially and temporally asynchronous and involves a limited number of cells in the xylem pericycle. To study the molecular regulation during pericycle activation, we developed a lateral root–inducible system. Successive treatments with an auxin transport inhibitor and exogenous auxin were used to prevent the first formative divisions and then to activate the entire pericycle. Our morphological and molecular data show that, in this inducible system, xylem pericycle activation was synchronized and enhanced to cover the entire length of the root. The results also indicate that the inducible system can be considered a novel in planta system for the study of synchronized cell cycle reactivation. In addition, the expression patterns of Kip-Related Protein2 (KRP2) in the pericycle and its ectopic expression data revealed that the cyclin-dependent kinase inhibitor plays a significant role in the regulation of lateral root initiation. KRP2 appears to regulate early lateral root initiation by blocking the G1-to-S transition and to be regulated transcriptionally by auxin.
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INTRODUCTION
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Lateral root formation plays a crucial role in plant development by permitting the construction of branched root systems. The process of lateral root formation consists of two major steps: cell cycle reactivation in the xylem pericycle and establishment of a new meristem (Celenza et al., 1995 ; Laskowski et al., 1995; Malamy and Benfey, 1997). In Arabidopsis, lateral roots are initiated by the local activation of pericycle cells at the xylem poles. Recently, we proposed a model to describe cell cycle progression that precedes the first formative divisions in lateral root initiation (Beeckman et al., 2001). In the xylem pericycle, basal cells proceed to G2 phase, whereas other pericycle cells remain in G1 phase. The first formative divisions in the pericycle depend on the basipetal transport of auxin, whereas shoot-derived auxin regulates the outgrowth of lateral roots (Casimiro et al., 2001; Bhalerao et al., 2002). It remains largely unknown how plants control the reactivation of the cell cycle during development, but it is generally accepted that plant hormones may play a central role. Plant hormones are known to affect the cell cycle directly, mainly at the transcriptional level (Stals and Inzé, 2001).
In all higher eukaryotes, including plants, activation of a cyclin-dependent kinase (CDK) A/cyclin D complex at the G1-to-S transition leads to hyperphosphorylation of the transcriptional repressor retinoblastoma protein (Soni et al., 1995; Meijer and Murray, 2000; Boniotti and Gutierrez, 2001). Inactivated retinoblastoma releases the transcription factor E2F/DP, which in turn triggers the expression of S phase–specific genes (Magyar et al., 2000; De Veylder et al., 2002; Kosugi and Ohashi, 2002). The next checkpoint, G2 to M, regulates cell cycle progression to the mitotic phase, mainly through B-type CDKs (CDKB1 and CDKB2) (Joubès et al., 2000; Boudolf et al., 2001) and A- and B-type cyclins (Renaudin et al., 1998; Mironov et al., 1999; John et al., 2001). Characteristically, cell cycle–regulatory proteins fluctuate during the cell cycle. Generally, this fluctuation is mediated by stringent transcriptional regulation and controlled proteolysis (Fobert et al., 1994; Shaul et al., 1996; Genschik et al., 1998). In addition, a class of CDK-inhibitory proteins, the Kip-related proteins (KRPs), is involved in inactivating CDK/cyclin complexes (Wang et al., 1997, 1998; De Veylder et al., 2001).
To understand the cell cycle regulation mechanisms that result in the initiation of new lateral roots, detailed molecular studies are required. However, the small number of cells involved in the first lateral root initiation events seriously hampers such studies (Taylor and Scheuring, 1994). Also, the lack of synchrony of the initiation events makes it very difficult to efficiently follow the development of lateral root initiation. To overcome these problems, we developed a system that allows the synchronization of the pericycle and enhances the activation of lateral root initiation. The system was based on seed germination in the presence of the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) and early transfer to the exogenous auxin 1-naphthalene acetic acid (NAA) to prevent and induce pericycle activation, respectively. With this approach, we were able to monitor synchronous cell cycle reactivation during early lateral root induction. Analysis of auxin distribution patterns in the system showed that auxin determines both the positioning and frequency of lateral root initiation. Our results suggested the G1-to-S checkpoint to be a target for auxin-mediated lateral root initiation. In addition, a CDK-inhibitory protein (KRP2) was shown to be regulated transcriptionally by auxin and to prevent lateral root initiation by blocking the G1-to-S transition.
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RESULTS
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Induction of Lateral Roots
To visualize cell cycle activity in the pericycle, we used the well-characterized marker line for active cell division, CYCB1;1::uidA, whose promoter activity also correlates well with the corresponding mRNA localization (Ferreira et al., 1994a, 1994b). In Arabidopsis, the first lateral root primordium is initiated  36 h after germination and is positioned in the basal half of the root (Beeckman et al., 2001) (Figures 1A and 1B)
. However, in a population of seedlings, this initiation event is spatially and temporally asynchronous. Furthermore, spontaneous lateral root initiation involves only a limited number of cells (Figures 1C and 1G), so it is burdensome to analyze in detail with molecular techniques. To study cell cycle progression during pericycle reactivation, we developed a lateral root–inducible system. The system is based on successive treatments with an auxin transport blocker (NPA) and exogenous auxin (NAA).
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Figure 1. CYCB1;1 Promoter Activity during Pericycle Activation for Lateral Root Initiation.
(A) No lateral root initiation sites were visible at 24 h after germination on MS medium.
(B) Spontaneous lateral root initiation at 36 h after germination on MS medium. The first lateral root initiation site is indicated with an arrowhead.
(C) Longitudinal anatomical section of the initiation site.
(D) Pericycle activation prevented on NPA.
(E) Pericycle activation after transfer from NPA to NAA for 12 h.
(F) Longitudinal anatomical section of a root after 10 h on NAA. Arrowheads indicate the newly formed anticlinal cell walls.
(G) Transverse section at 36 h after germination on MS medium.
(H) Transverse section after 10 h of NAA treatment in a dark field. GUS staining is shown as purple.
(I) Transverse section after 12 h of NAA treatment. Periclinal divisions are indicated with red arrowheads.
Asterisks indicate adventitious root primordia. c, cortex; e, epidermis; en, endodermis; p, pericycle. Bars = 1 mm for (A), (B), (D), and (E); 0.1 mm for (C) and (F); and 0.05 mm for (G) to (I). Large arrowheads in (G) to (I) indicate xylem pole pericycle cells.
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In the inducible system, seeds were germinated on NPA-containing medium to prevent the formative divisions in the pericycle (Casimiro et al., 2001). The optimal NPA concentration was determined by comparing the lateral root induction rate on 1 and 10 µM NPA-containing medium with that of seedlings grown on Murashige and Skoog (MS) medium. After 48 h on 1 µM NPA medium, generally one lateral root was initiated per seedling, whereas on MS medium, three primordia were visualized by CYCB1;1::uidA promoter activity. However, on 10 µM NPA, no lateral root initiation sites were detectable after 72 h of growth (Figure 1D). NPA also prevented the activation of adventitious root primordia at the root-hypocotyl junction. Growth for 72 h on NPA provided sufficiently long main roots (5 mm) to collect samples but did not induce the changes in pattern and polarity described by Sabatini et al. (1999). The 10 µM concentration of NPA was used in all experiments described below. For the inducible system, after germination, seedlings were grown on NPA for 3 days (72 h). These 3-day-old seedlings were considered to be at time point 0 for the inducible system. After treatment with NPA, seedlings were transferred to medium containing exogenous auxin (10 µM NAA) for 12 h until the entire pericycle was activated, as indicated by uniform CYCB1;1 promoter activity (Figure 1E). On NAA, induction of the formative divisions for lateral root initiation involved both xylem pericycle strands (Figures 1F and 1H). From the first round of anticlinal divisions, the development of the xylem pole pericycle cells proceeded to periclinal divisions (Figure 1I) (Malamy and Benfey, 1997).
Auxin Response in the Inducible System
Because lateral root initiation is known to be regulated by auxin, we tested the distribution kinetics of auxin responsiveness and cell cycle activity during NPA and NAA treatment. If auxin determined the position of lateral root initiation, the sequence of initiation would follow the primary direction of the auxin flow. Also, if the amount of applied auxin affected the frequency of lateral root initiation sites, there would be a difference in lateral root numbers between the different treatments. To test these hypotheses, marker lines for auxin responsiveness (DR5::uidA; Ulmasov et al., 1997) and cell division activity (CYCB1;1::uidA) were used in a set of transfer experiments. Because NPA accumulates auxin in the root apex (Casimiro et al., 2001), a flow of endogenous auxin is expected to move basipetally from the root tip upon release from the NPA block. In our experiments, the seedlings were transferred from NPA to MS medium or from MS medium to NAA and were stained for  -glucuronidase (GUS) activity every 2 h. To estimate the timing of auxin penetration in the tissues, the DR5::uidA line also was transferred from NPA to NAA for durations of 0.5, 1, 1.5, 2, and 4 h and stained for GUS activity.
On NPA (72 h after germination), DR5::uidA promoter activity in the roots was restricted to the root apical meristem (Figure 2A) . When transferred from NPA to NAA, DR5::uidA promoter activity was induced at 1.5 h in the apical region of the root and already covered the entire root length at 3 h (Figures 2B and 2C, respectively). After treatment for 72 h on NPA followed by 6 hr on MS medium, DR5::uidA promoter activity was present in the apical half of the root (Figures 2D and 2E) and proceeded basipetally in the root during further incubation on MS medium. When CYCB1;1::uidA seedlings were transferred from NPA to MS medium, no clear induction in the pericycle was observed by GUS activity, even after 6 h (Figure 2F). At 10 h, individual lateral root initiation sites were detected in the apical half of the root (Figure 2G). By contrast, in seedlings transferred from MS medium (after 24 h of growth) to NAA, individual lateral root initiation sites at 4 h were observed to be positioned in the basal half of the root (Figure 2H). Only later, after 6 h on NAA, were lateral roots also initiated in the apical half of the root (Figure 2I). From 8 h onward, the entire pericycle showed GUS activity (Figure 2J). In conclusion, pretreatment with NPA resulted in the relocalization of lateral root initiation sites to the apical half of the root, whereas in the absence of NPA, the first lateral roots initiated in the basal half of the root.
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Figure 2. Histochemical GUS Staining Patterns of DR5::uidA and CYCB1;1::uidA in Transfer Experiments from NPA to NAA, from NPA to MS Medium, and from MS Medium to NAA.
(A) DR5::uidA on NPA. The arrow indicates the root apical meristem.
(B) DR5::uidA after transfer from NPA to NAA for 1.5 h.
(C) DR5::uidA after transfer from NPA to NAA for 3 h.
(D) DR5::uidA after transfer from NPA to MS medium for 6 h.
(E) DR5::uidA after transfer from NPA to MS medium for 6 h (detailed image).
(F) CYCB1;1::uidA after transfer from NPA to MS medium for 6 h.
(G) CYCB1;1::uidA after transfer from NPA to MS medium for 10 h. The arrow indicates the first lateral root initiation site at the apical end of the root.
(H) CYCB1;1::uidA after transfer from MS medium to NAA for 4 h. Arrows indicate the first initiation sites in the basal half of the root.
(I) CYCB1;1::uidA after transfer from MS medium to NAA for 6 h. The lateral root initiation sites are along the entire length of the root. Arrows indicate developing lateral root primordia.
(J) CYCB1;1::uidA after transfer from MS medium to NAA for 8 h. The entire pericycle is activated.
Bars = 1 mm.
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Cell Cycle Activity in the Induced Roots
The fact that the cell cycle reactivation of all xylem pericycle cells of NPA-pretreated roots transferred to NAA medium was rapid and uniform indicated that the entire pericycle was synchronized at the same cell cycle phase on NPA medium. To identify the cell cycle phase in which the xylem pericycle cells were arrested, a cell cycle blocker, hydroxyurea (HU), was applied in the inducible system. HU is an inhibitor of ribonucleotide diphosphate reductase and blocks the cell cycle during the G1-to-S transition (Planchais et al., 2000). If the xylem pericycle cells were blocked at the G1 phase on NPA treatment, no progression to the G2-to-M transition would take place and no CYCB1;1 promoter activity would be detected when transferred to NAA in the presence of HU. On the other hand, if the pericycle cells were blocked at the G2 phase, a first round of cell divisions could take place, as visualized by CYCB1;1 promoter activity (Beeckman et al., 2001). To test the effects of HU on cell cycle progression in the inducible system, seedlings of the CYCB1;1::uidA line were germinated and grown for 48 h on NPA, then they were transferred to NPA medium containing 100 mM HU. After another 24-h growth period, seedlings were transferred to NAA containing the same concentration of HU. Pericycle activation was evaluated based on CYCB1;1 promoter activity. On NAA supplemented with 100 mM HU, pericycle activation was prevented, as seen by the absence of induction of CYCB1;1 promoter activity at 12 h (Figure 3A)
compared with 12 h of NAA treatment alone (Figure 1E). This result indicates that on NPA, the xylem pericycle was blocked in the G1 phase. In the root apical meristem, CYCB1;1 promoter activity was reduced and showed patchy patterns, indicating that the cells were in different cell cycle stages in the meristem when transferred onto HU (data not shown).
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Figure 3. Histochemical GUS Assays of CDKA;1, CYCA2;1, and CYCB1;1 Promoter Activities in a Time-Course Experiment with NPA and NAA.
(B) to (H) show the promoter activities of CDKA;1::uidA and CYCA2;1::uidA on NPA- and NAA-treated roots with differential interference contrast microscopy. (A), (I) to (N), and (P) show the activities of CYCB1;1::uidA by stereomicroscopy.
(A) CYCB1;1 promoter activity in roots treated with NAA and 100 mM HU for 12 h (cf. with [N]).
(B) CDKA;1::uidA promoter activity in the pericycle on NPA.
(C) CDKA;1::uidA promoter activity after 12 h on NAA. There was no change compared with (B).
(D) CYCA2;1::uidA seedlings treated for 72 h with NPA. Strong promoter activity was limited to the central stele. Low staining or diffusion are seen in the pericycle, endodermis, and cortex.
(E) CYCA2;1::uidA seedlings treated for 4 h with NAA. No expression is seen in the xylem pericycle.
(F) CYCA2;1::uidA seedlings treated for 6 h with NAA. Expression is emerging in the xylem pericycle.
(G) CYCA2;1::uidA seedlings treated for 8 h with NAA. The first asymmetric divisions are visualized with strong CYCA2;1::uidA promoter activity. Arrowhead indicates a newly formed cell wall resulting from an asymmetrical division.
(H) CYCA2;1::uidA seedlings treated for 10 h with NAA. A fully stained pericycle consisting of small radially expanded cells is seen.
(I) No induction of CYCB1;1::uidA activity at 0 h.
(J) No induction of CYCB1;1::uidA activity at 4 h.
(K) Induction of CYCB1;1::uidA activity at 6 h.
(L) CYCB1;1::uidA activity at 8 h.
(M) CYCB1;1::uidA activity at 10 h.
(N) CYCB1;1::uidA activity at 12 h.
(O) A seedling kept on NAA for 1 week. Lateral root induction along the entire length of the root at the two opposite xylem poles of the pericycle is seen.
c, cortex; e, epidermis; en, endodermis; p, pericycle; x, xylem. Bars = 0.1 mm for (B) to (H) and 1 mm for (A), (I) to (N), and (O).
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To study cell cycle progression during pericycle reactivation, promoter activity in CDKA;1::uidA, CYCA2;1::uidA, and CYCB1;1::uidA fusion lines was evaluated. CDKA;1 promoter activity reflects the state of competence for cell division activity or an undifferentiated state (Martinez et al., 1992; Hemerly et al., 1993). CYCA2;1 promoter activity was used as a marker for the late S and G2 phases of the cell cycle (Burssens et al., 2000a), whereas CYCB1;1 promoter activity marked progression through late G2 to M phase (Ferreira et al., 1994b). Whole-mount GUS assay samples were prepared from each line at 0, 4, 6, 8, 10, and 12 h after transfer from NPA to NAA. CDKA;1 promoter activity in the xylem pericycle was strong at all time points, including in the NPA-treated samples (Figures 3B and 3C). Strong CDKA;1::uidA expression also covered the central stele. The two cyclin promoters revealed a defined pattern of cell cycle progression in the pericycle. On NPA, the promoter activity of CYCA2;1 was limited to the root apical meristem and vascular parenchyma (Figure 3D). After transfer to NAA from 4 to 6 h, CYCA2;1 promoter activity started to emerge in the xylem pericycle as a sign of progression to G2 phase (Figures 3E and 3F). At 8 h, the expression marked the first asymmetric divisions in the apical half of the xylem pericycle (Figure 3G), and at 10 h, uniform expression was observed in the small radially expanded xylem pericycle cells (Figure 3H). At 12 h, the apical part of the xylem pericycle approached the two-cell-layer stage, or stage II (Malamy and Benfey, 1997), and CYCA2;1 promoter activity remained strong in the tissues (data not shown). The expression pattern started from the apical half of the root and gradually covered the basal half of the root (data not shown).
As a marker for the G2-to-M phase of the cell cycle, CYCB1;1 promoter activity had a delayed pattern compared with that of CYCA2;1. On NPA medium, no CYCB1;1 promoter activity was detected above the root apical meristem (Figure 3I). After seedlings had been transferred to NAA, CYCB1;1 promoter activity was induced gradually from 6 h on and proceeded basipetally in the xylem pericycle (Figures 3J to 3M). No individual lateral root initiation sites were detected; instead, at 12 h, the whole xylem pericycle showed strong CYCB1;1 promoter activity as a sign of a fully activated pericycle (Figure 3N). In the whole-mount GUS-stained samples, the CYCB1;1::uidA expression is seen as two strands of blue staining, which represent the xylem pole pericycle cell files shown in Figures 1F and 1H. When seedlings remained on NAA for 1 week, lateral roots were induced along the entire length of the root at the two opposite xylem poles of the pericycle (Figure 3O).
Cell Cycle Regulation during Early Lateral Root Initiation
Semiquantitative reverse transcription (RT) PCR was used to study the expression of cell cycle–regulatory genes during pericycle activation in our system. The expression of several well-characterized cell cycle genes corresponded to synchronous cell cycle progression (Figure 4A)
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Figure 4. Cell Cycle Gene Expression during Lateral Root Initiation.
(A) RT-PCR gel blots showing the transcript levels of HISTONE H4, E2Fa, CYCD1;1, CYCD3;1, CYCA2;1, CYCB1;1, CYCB2;1, CDKA;1, CDKB1;1, CDKB2;1, CDKB2;2, KRP1, KRP2, KRP3, KRP4, and ACTIN from 72 h on NPA (0 h) to 12 h on NAA.
(B) Cell cycle progression as predicted from the transcript profiles in (A) and indicated by arrows together with the current cell cycle phase: G1 (gap 1 phase), G1/S (G1-to-S phase transition), G2/M (G2-to-M phase transition), and M (mitosis).
(C) RT-PCR gel blot of KRP2 transcripts in a short time course.
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In the inducible system, at 0 h (72 h on NPA), no or low expression of marker genes for the active cell cycle was detected. At 4 h, cell cycle marker genes for the G1-to-S transition, HISTONE H4 and E2Fa, were induced along with the CYCD3;1 cyclin. Unexpectedly, the B-type CDKs CDKB1;1 and CDKB2;1 followed the same pattern. However, the transcript levels showed clear peaks at 8 h, as in other B-type CDKs. The G1-to-S and S phase–specific cyclins CYCD1;1 and CYCA2;1 were induced only at 6 h, although their transcripts were seen weakly at 0 and 4 h. The low level of CYCA2;1 transcripts at these early time points correlates with the constitutive promoter activity observed in the vascular cylinder (Figure 3). At 6 h, genes involved in the G2-to-M transition, CYCB1;1, CYCB2;1, CDKB1;1, and CDKB2;2, showed simultaneous induction. CDKA;1 transcripts were present constitutively from time point 0. Remarkably, three of the CDK inhibitor genes had a pattern opposite that of the other cell cycle–regulatory genes. The transcript levels of KRP1 and KRP2 genes were high at 0 h but were downregulated after 4 h on NAA. The KRP4 gene responded less strongly: the transcripts were present at 0 h but were reduced only slightly at 4 h. The transcript profiles of the KRP3 genes deviated from those of the other KRP genes. The transcript levels were low at 0 h, and clear induction was observed at 4 h. The actin-2 gene was used to evaluate equal input of RNA in the analysis. Figure 4B highlights the postulated cell cycle progression with arrows, according to the transcript profiles.
In Situ Expression Pattern of KRP2 mRNA
Because expression of the KRP1 and KRP2 genes was high in NPA-treated roots, KRPs may be involved in preventing pericycle activation for lateral root formation. The tissue-specific localization of KRP2 mRNA was analyzed in wild-type Arabidopsis and radish roots. In sections from Arabidopsis roots treated in the inducible system, strong KRP2 expression was observed in pericycle cells in the NPA treatment (Figure 5A)
, whereas it disappeared almost completely by the subsequent NAA treatment (Figure 5B). This result indicates that the transcript accumulation of KRP2 was affected directly by the application of auxin.
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Figure 5. KRP2 Expression in Root Tissues.
In situ hybridization on Arabidopsis and radish roots performed with a 35S-UTP–labeled KRP2 antisense riboprobe. Hybridization signals are presented as red dots.
(A) KRP2 mRNA localization in an Arabidopsis root treated with NPA (72 h).
(B) KRP2 mRNA localization in an Arabidopsis root treated with NAA (12 h).
(C) Longitudinal section of lateral root primordia in an Arabidopsis root.
(D) Toluidine blue–stained cross-section of young parts of a radish root. KRP2 expression was found mainly in pericycle cells excluding the xylem poles. Arrows (D) to (G) indicate protoxylem poles.
(E) KRP2 expression at the phloem pole of the pericycle.
(F) KRP2 expression at the xylem and the phloem poles of the pericycle.
(G) KRP2 expression around the entire pericycle.
(H) Number of lateral roots per centimeter in wild-type and 35S-KRP2 seedlings.
(I) Total root length of wild-type and 35S-KRP2 seedlings.
(J) 35S-KRP2 line 72 h after germination on NPA medium, showing CYCB1,1::uidA activity.
(K) 35S-KRP2 line 12 h after transfer from NPA to NAA medium, showing CYCB1,1::uidA activity.
WT, wild type. Bars = 0.1 mm for (A) to (C), 0.05 mm for (D) to (G), and 1 mm for (J) and (K).
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The direct effect of auxin on KRP2 expression was confirmed further by RT-PCR data from a short-time-course experiment (0, 1, 1.5, 2, 3, and 4 h on NAA after incubation on NPA) in which KRP2 expression was downregulated already 1.5 h after transfer to NAA (Figure 4C). At that time point, DR5::uidA expression revealed that auxin had penetrated the root tissues initially (as described above). These results again indicate that KRP2 levels are essentially under transcriptional control.
In transverse sections of young parts of radish seedling roots (recognizable by the lack of xylem differentiation in the center of the stele), phloem pericycle-specific expression for the KRP2 gene was observed (Figure 5D). Interestingly, no transcripts were detected at protoxylem poles (i.e., the sites at which lateral root initiation normally takes place). However, in mature parts of radish roots (with fully differentiated xylem), the expression had more variable patterns. In different sections, the signal was detected at one phloem pole of the pericycle (Figure 5E), at xylem and phloem poles (Figure 5F), or around the entire pericycle (Figure 5G). It is remarkable that KRP2 expression was seen in pericycle cells opposite developing lateral root primordia (Figure 5C). As such, the spatial expression pattern of KRP2 supports the hypothesis that KRP2 plays a role in regulating cell cycle activity in root pericycle cells.
Lateral Root Initiation in the 35S-KRP2 Line
Recently, the effects on leaf development and cell cycle duration of KRP2 overexpression have been studied in detail (De Veylder et al., 2001). To evaluate further the postulated involvement of KRP2 in the regulation of early lateral root initiation, the effects of ectopic expression were studied. The total root length and the number of lateral root primordia of two 35S-KRP2 transgenic lines and wild-type plants were counted after 2 weeks of growth. The number of lateral roots in the 35S-KRP2 line was reduced by >60% compared with that in the wild type, whereas total root length was affected only slightly at this age (Figures 5H and 5I). To exclude the possibility that KRP2 overexpression still allowed the cell cycle to be induced in the presence of increased auxin concentration, cell cycle activity in the 35S-KRP2 pericycle was analyzed in the inducible system. To visualize the effect of KRP2 overexpression on pericycle activation, the CYCB1;1::uidA marker gene was introduced into the overexpressing line by crossing. In this double transgenic line, no CYCB1;1::uidA induction was detected after 12 h of treatment on NAA (Figures 5J and 5K). This result essentially confirms that KRP2 prevents cell cycle activation for formative divisions in the xylem pericycle.
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DISCUSSION
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Auxin Determines the Positioning and Frequency of Lateral Root Initiation
In a previous report, unique cell cycle regulation was shown to occur in the xylem pericycle, in which cells proceed to G2 phase, whereas the rest of the pericycle remained at G1 phase (Beeckman et al., 2001). Cell cycle regulation in the xylem pericycle is known to be mediated by auxin because the inhibition of polar auxin transport effectively blocks the first formative divisions for lateral root initiation (Casimiro et al., 2001). Auxin also has been reported to affect cell cycle activity (Stals and Inzé, 2001). Our RT-PCR results demonstrate clearly that auxin promotes lateral root initiation by cell cycle stimulation at the G1-to-S transition. This auxin-mediated effect on the cell cycle also has been suggested by previous work in various species and experimental systems (Corsi and Avanzi, 1970; Nougarede and Rondet, 1983; Chriqui, 1985).
In addition, the amount and direction of auxin flow in the roots was shown to determine the frequency and position of lateral root initiation. On NPA, DR5 promoter activity was restricted to the root apical meristem, where expression was very strong, indicating that NPA blocked auxin transport from the root tip and caused its accumulation in the meristem (Müller et al., 1998; Casimiro et al., 2001). Fast induction of DR5 promoter activity was observed in the pericycle after release from the NPA block, because the accumulated auxin reserves in the root tips were redistributed rapidly in the root. Auxin redistribution was followed by the induction of CYCB1;1 promoter activity with a delay. In the two transfer experiments, the number of induced lateral roots depended on low or high concentrations of auxin in the transfer from NPA to MS medium and from NPA to NAA, respectively. Depriving roots of auxin during NPA treatment also appeared to prevent the typical localization of lateral root initiation in the basal half of the root (Beeckman et al., 2001). In both cases (NPA to MS medium and NPA to NAA), the pericycle induction was relocalized to the apical half of the root. By contrast, when transferred from MS medium to NAA, the first lateral root induction sites appeared normally in the basal half of the roots, suggesting that the free endogenous auxin is the only determinative factor for the pericycle to prime the spontaneous lateral root initiation. This finding also implies that lateral root initiation could occur independently of positional control mechanisms from the surrounding tissues.
Pericycle-Specific Expression of KRP2 mRNA Is Regulated by Auxin
KRP1 and KRP2 expression were high in the inactive pericycle of NPA-treated roots. Also, during cell cycle arrest caused by sugar starvation, KRP2 transcript levels are high (Menges and Murray, 2002). Upon transfer to NAA, strong downregulation of KRP2 and KRP1 followed. Similarly, the KRP4 gene also had a weak negative response to the transfer to auxin. Previously, auxin was shown to negatively affect KRP2 expression in Arabidopsis cell suspensions, whereas KRP1 did not respond (Richard et al., 2001). In NPA and NAA treatments, the response of KRP3 was opposite, being induced upon transfer to auxin. KRP3 also is highly expressed in actively dividing cell suspension cultures (De Veylder et al., 2001; Menges and Murray, 2002), and unlike KRP1, it does not respond to the growth-inhibiting hormone abscisic acid (Wang et al., 1998). In conclusion, KRP3 may play a role in the active cell division cycle, deviating significantly from other KRPs analyzed to date.
In in situ hybridization of KRP2 mRNA, the expression patterns showed clearly variable tissue-specific localization depending on the developmental stage of the sample tissue. In young tissues, in which lateral roots are initiated preferentially (Blakely et al., 1982), the expression appeared to be restricted to the phloem pericycle. In older tissues, in which normally no new lateral roots are formed, the expression was seen at xylem poles or around the whole pericycle. Interestingly, KRP2 expression was observed opposite a developing lateral root primordium. Indeed, under normal conditions, lateral roots are never formed in opposite positions. This variability in the localization of expression may reflect the spatially and temporarily variable competence of the pericycle for lateral root development.
For some of the KRPs (KRP1 and KRP2), interaction with CDKA;1 and inhibition of its kinase activity have been shown (Wang et al., 1998; De Veylder et al., 2001). In Arabidopsis roots, CDKA;1 also is expressed in tissues that do not divide actively but are competent for cell division (Hemerly et al., 1993). During pericycle activation, CDKA;1 transcripts and promoter activity were detected on NPA treatment (i.e., in the inactive pericycle), indicating that the pericycle remains competent for cell divisions. The active cell cycle was inhibited, and at the same time, both KRP1 and KRP2 were highly expressed. From 4 h onward, KRP2 transcript levels decreased sharply, whereas those of CDKA;1 remained high and were accompanied by the accumulation of other marker genes for the active cell cycle. One putative role for KRPs might be to keep the constitutively transcribed and possibly translated CDKA kinases inactive, because even in the absence of correct cyclin subunits, kinases might be activated by nonspecific cyclins.
In mammalian cells, CDK-inhibiting proteins appear at high levels during the G0 and G1 arrests (Pagano et al., 1995). The levels decrease at entry into the cell cycle, however, without change in the constant levels of transcripts and protein synthesis. This observation indicates that, in mammals, the inhibitory proteins are targeted for proteolysis, mediated by a ubiquitin-dependent pathway (Pagano et al., 1995). In plants, auxin has been shown to be involved in the SCFtir-regulated ubiquitination-dependent proteolytic pathway (Gray et al., 1999). However, no data are available on the accumulation of KRP proteins in plants. In contrast to mammalian systems, plant KRPs appear to be controlled more at the transcriptional level, which may indicate fundamental differences in the regulation of these inhibitors.
Ectopic Expression of KRP2 Strongly Affects Pericycle Activation
In animals, CDK inhibitors such as Kip/Cip p27 have been proposed as links between the developmental control of cell proliferation and morphological developments (Chen and Segil, 1999). In plants, KRP1 and KRP2 overexpression causes reduction in organ growth and specific developmental defects in leaves (Wang et al., 2000; De Veylder et al., 2001). In our study, KRP2 overexpression prevented pericycle activation and reduced the number of lateral roots by >60%. In NAA treatment, the 35S-KRP2 line failed to induce CYCB1;1::uidA expression even after 12 h of incubation. These results clearly show that KRP2 specifically prevents cell cycle induction for formative divisions of lateral roots in the pericycle. During spontaneous lateral root initiation, the xylem pericycle cells are known to proceed to the G2 phase of the cell cycle before lateral root initiation (Blakely et al., 1982; Beeckman et al., 2001). This development takes place in the basal half of the root, where later lateral roots are initiated locally (Beeckman et al., 2001). Based on our results from the inducible system, we postulate that during spontaneous lateral root formation, KRP2 plays an active role in regulating the G1-to-S transition in the pericycle in an auxin-dependent manner. When the developmental signal, auxin, is absent, the pericycle activation is prevented by KRP2, and upon the auxin signal, pericycle activation becomes possible via the downregulation of KRP2. During plant development, the pericycle competence for lateral root development appears to vary depending on the maturation state of the root. This variability correlated well with the KRP2 mRNA expression patterns described previously.
Synchronous Cell Cycle Progression during Pericycle Activation
The analysis of transcript profiles and promoter activities of cell cycle–regulatory genes in this system demonstrated that synchronous cell cycle progression occurred during pericycle activation. The expression profiles are very consistent with those described for a partially synchronized Arabidopsis cell culture (Menges and Murray, 2002). These results suggest that the system could be used as a tool complementary to cell suspension cultures for the analysis of synchronous cell cycle progression in plants.
Extensive research on lateral root initiation has revealed several genes and gene products that are important at various phases of root development. However, we still do not thoroughly understand the regulatory pathways that lead to lateral root initiation. The difficulties may result from the apparent spatial and temporal asynchrony of the initiation events (Malamy and Ryan, 2001). Here, we developed an inducible system in which the pericycle was synchronized for lateral root development in an enhanced manner. The effect of this enhanced synchronization differs essentially from the more arbitrary lateral root induction induced by the exogenous application of auxin alone. This system allowed detailed histological and molecular analysis of early lateral root initiation events. Therefore, we propose this system as a fundamental approach for the study of the early molecular regulation of lateral root initiation. Currently, we are performing genome-wide expression analysis with this inducible system using microarray (www.microarray.be) and cDNA-amplified fragment length polymorphism techniques. Our preliminary results indicate that the system will allow us to identify and sort regulatory genes involved in the early processes of root branching.
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METHODS
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Plant Material and Growth Conditions
The transgenic line CYCB1;1::uidA of Arabidopsis thaliana in a C24 background (Ferreira et al., 1994b) was used for all experiments unless indicated otherwise. For histochemical -glucuronidase (GUS) assays, the other transgenic lines were CDKA;1::uidA (Hemerly et al., 1993), CYCA2;1::uidA (Burssens et al., 2000a), and DR5::uidA (Ulmasov et al., 1997). Medium containing N-1-naphthylphthalamic acid (NPA) and 1-naphthalene acetic acid (NAA) were prepared from Murashige and Skoog (1962) germination medium as described by Valvekens et al. (1988). Seeds were plated on vertically oriented square plates (Greiner Labortechnik, Frickenhausen, Germany). Plants were grown in a growth chamber under continuous light (110 µE·m-2·s-1 PAR supplied by cool-white fluorescent tungsten tubes [Osram, München, Germany]) at 22°C. For the time-course experiments, plants were germinated on 10 µM NPA, and the seedlings were grown for 72 h on NPA before they were transferred to NAA-containing medium. Pericycle reactivation was followed every 2 h from 4 to 12 h. For the KRP2 gene and the DR5::uidA line, an earlier time course also was used (0, 0.5, 1, 1.5, 2, and 4 h). For the hydroxyurea experiment, 100 mM hydroxyurea was added to the NPA and NAA media. Sample material was collected at different time points for the various assays.
Histochemical GUS Assays
Complete seedlings or root cuttings were stained in multiwell plates (Falcon 3043; Becton Dickinson, Bedford, MA). GUS assays were performed as described by Beeckman and Engler (1994). Samples mounted in Tris-saline buffer or lactic acid were observed and photographed using a stereomicroscope (Stemi SV11; Zeiss, Jena, Germany) or by a differential interference contrast microscope (Leica, Vienna, Austria).
Microscopy
For anatomical sections, GUS-stained samples were fixed overnight in 1% glutaraldehyde and 4% paraformaldehyde in 50 mM phosphate buffer, pH 7. Samples were dehydrated and embedded in Technovit 7100 resin (Heraeus Kulzer, Wehrheim, Germany) according to the manufacturer's protocol. For proper orientation of the samples, transparent strips were used to facilitate tissue alignment (Beeckman and Viane, 2000). Sections of 5-µm samples were cut with a microtome (Minot 1212; Leitz, Wetzlar, Germany), dried on object glasses, and counterstained for cell walls with 0.05% ruthenium red (Fluka Chemica, Buchs, Switzerland) in tap water for 30 s. After drying overnight, the sections were mounted in DePex medium (British Drug House, Poole, UK) and covered with cover slips for analysis and photography.
Reverse Transcription PCR
Endogenous transcript levels of a set of cell cycle–regulatory genes were analyzed during the NPA and NAA treatments by semiquantitative reverse transcription PCR as described by Burssens et al. (2000b). Only the lateral root–inducible segments were used; therefore, the root apical meristems were cut off, and the shoots were removed by cutting below the adventitious root primordia. Total RNA was extracted with Trizol (Invitrogen, Gaithersburg, MD) from 300 excised root segments per sample. cDNA was prepared from 1-µg total RNA samples in a volume of 40 µL using the Superscript RT II first-strand cDNA synthesis kit (Invitrogen). To verify the exponential phase of PCR amplification, 15 and 20 or 18 and 23 cycles were tested for each gene. The primers used in the PCR reactions for CYCA2;1, CYCB1;1, CYCB2;1, CYCD1;1, CYCD3;1, CDKA;1, KRP1, KRP2, KRP3, KRP4, and E2Fb were as described by Richard et al. (2002); those used for CDKB1;1, CDKB1;2, CDKB2;1, and CKDB2;2 were as described by Boudolf et al. (2001); and that used for HISTONE H4 was as described by Magyar et al. (2000). The gene encoding actin-2 was used as a control, with primers 5'-GTTGCACCACCTGAAAGGAAG-3' and 5'-CAATGGGACTAAAACGCAAAA-3'.
mRNA in Situ Hybridization
Nearly all steps of the in situ method were performed as described by de Almeida Engler et al. (2001). Radish (Raphanus sativus) and Arabidopsis seedlings were germinated on K1 medium (Valvekens et al., 1988), and plant material was collected for fixation. Samples were fixed in 2.5% glutaraldehyde, dehydrated, and embedded in paraffin. Sections (10 µm thick) were fixed to 3-aminopropyltriethoxy-silane–coated slides and used during the in situ hybridization procedure. Gene-specific antisense and sense probes of KRP2 were synthesized from PCR products flanked by T7 and Sp6 promoters, and 15 x 106 cpm/slide was applied (75 ng/mL). Exposure times varied, and slides containing radish tissues always were developed before Arabidopsis slides. Images were created using a digital Axiocam (Zeiss) under standard bright-field optics.
Analysis of the KRP2-Overexpressing Line
To analyze lateral root development, KRP2-overexpressing seedlings (n = 40) from two independent transgenic lines were grown for 2 weeks on vertical plates together with wild-type plants (n = 15) (both lines were in the Columbia ecotype). Digital images of the root systems were obtained by scanning the plates with a flat-bed scanner. Total root length and number of lateral root primordia were counted per centimeter with Scion Image for Windows (Scion Corp., Frederick, MD). To visualize the effects of KRP2 overexpression on pericycle activation, the 35S-KRP2 line was crossed with the CYCB1;1::uidA line. The F2 population was treated according to the inducible system. Homozygous mutants were selected according to the shoot phenotype (De Veylder et al., 2001) and stained for GUS activity as described above.
Upon request, all novel materials described in this article will be made available in a timely manner for noncommercial research purposes. No restrictions or conditions will be placed on the use of any materials described in this article that would limit their use for noncommercial research purposes.
Accession Number
The accession number for the gene encoding actin-2 is U37281.
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Acknowledgments
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The authors thank all of the students who contributed to this work: Kirsten Kuijpers, Ive De Smet, and Robim Marcelino Rodrigues. Lieven De Veylder and co-workers are thanked for providing us with the 35S-KRP2 line. Tom Guilfoyle (University of Missouri, Columbia) is thanked for the DR5::uidA line. Christophe Reuzeau (CropDesign, Gent, Belgium) is acknowledged for critical review of the manuscript, and Martine De Cock is thanked for help in preparing it. Jill Rupnow is greatly acknowledged for reading the manuscript. This research was supported by grant P5/13 from the Interuniversity Poles of Attraction Program (Belgian State, Prime Minister's Office, Federal Office for Scientific, Technical, and Cultural Affairs). K.H. is indebted to the Academy of Finland and the Finnish Cultural Foundation for fellowships.
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Footnotes
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Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.004960.
1 Current address: Laboratoire de Cytologie Expérimentale et Morphogenèse Végétale, Université Pierre et Marie Curie, F-75252 Paris Cedex 05, France. 
Received June 3, 2002;
accepted July 10, 2002.
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References
|
|---|
Beeckman, T., Burssens, S., and Inzé, D. (2001). The peri-cell-cycle in Arabidopsis. J. Exp. Bot. 52, 403–411.[Abstract/Free Full Text]
Beeckman, T., and Engler, G. (1994). An easy technique for the clearing of histochemically stained plant tissue. Plant Mol. Biol. Rep. 12, 37–42.
Beeckman, T., and Viane, R. (2000). Embedding of thin plant specimens for oriented sectioning. Biotechnol. Histochem. 75, 23–26.
Bhalerao, R., Eklöf, J., Ljung, K., Marchant, A., Bennett, M., and Sandberg, G. (2002). Shoot derived auxin is essential for early lateral root emergence in Arabidopsis seedlings. Plant J. 29, 325–332.[CrossRef][Web of Science][Medline]
Blakely, L.M., Durham, M., Evans, T.A., and Blakely, R.M. (1982). Experimental studies on lateral root formation in radish seedling roots. I. General methods, developmental stages, and spontaneous formation of laterals. Bot. Gaz. 143, 341–352.[CrossRef]
Boniotti, M.B., and Gutierrez, C. (2001). A cell-cycle-regulated kinase activity phosphorylates plant retinoblastoma protein and contains, in Arabidopsis, a CDKA/cyclin D complex. Plant J. 28, 341–350.[CrossRef][Web of Science][Medline]
Boudolf, V., Rombauts, S., Naudts, M., Inzé, D., and De Veylder, L. (2001). Identification of novel cyclin-dependent kinases interacting with the CKS1 protein of Arabidopsis. J. Exp. Bot. 52, 1381–1382.[Abstract/Free Full Text]
Burssens, S., de Almeida Engler, J., Beeckman, T., Richard, C., Shaul, O., Ferreira, P., Van Montagu, M., and Inzé, D. (2000a). Developmental expression of the Arabidopsis thaliana CycA2;1 gene. Planta 211, 623–631.[CrossRef][Web of Science][Medline]
Burssens, S., Himanen, K., van de Cotte, B., Beeckman, T., Van Montagu, M., Inzé, D., and Verbruggen, N. (2000b). Expression of cell cycle regulatory genes and morphological alterations in response to salt stress in Arabidopsis thaliana. Planta 211, 632–640.[CrossRef][Web of Science][Medline]
Casimiro, I., Marchant, A., Bhalerao, R.P., Beeckman, T., Dhooge, S., Swarup, R., Graham, N., Inzé, D., Sandberg, G., Casero, P.J., and Bennett, M. (2001). Auxin transport promotes Arabidopsis lateral root initiation. Plant Cell 13, 843–852.[Abstract/Free Full Text]
Celenza, J.L., Jr., Grisafi, P.L., and Fink, G.R. (1995). A pathway for lateral root formation in Arabidopsis thaliana. Genes Dev. 9, 2131–2142.[Abstract/Free Full Text]
Chen, P., and Segil, N. (1999). p27Kip1 links cell proliferation to morphogenesis in the developing organ of Corti. Development 126, 1581–1590.[Abstract]
Chriqui, D. (1985). Induction de prolifération des cellules prérhizogènes: Auxine et polyamines. Bull. Soc. Bot. Fr. 132, 127–141.
Corsi, G., and Avanzi, S. (1970). Cytochemical analyses on cellular differentiation in the root tip of Allium cepa. Caryologia 23, 381–394.
de Almeida Engler, J., De Groodt, R., Van Montagu, M., and Engler, G. (2001). In situ hybridization to mRNA of Arabidopsis tissue sections. Methods 23, 325–334.[CrossRef][Web of Science][Medline]
De Veylder, L., Beeckman, T., Beemster, G., de Almeida Engler, J., Ormenese, S., Maes, S., Naudts, M., Van Der Schueren, E., Jacqmard, A., Engler, G., and Inzé, D. (2002). Control of proliferation endoreduplication and differentiation by the Arabidopsis E2Fa-Dpa transcription factor. EMBO J. 21, 1360–1368.[CrossRef][Web of Science][Medline]
De Veylder, L., Beeckman, T., Beemster, G.T.S., Krols, L., Terras, F., Landrieu, I., Van Der Schueren, E., Maes, S., Naudts, M., and Inzé, D. (2001). Functional analysis of cyclin-dependent kinase inhibitors of Arabidopsis. Plant Cell 13, 1653–1667.[Abstract/Free Full Text]
Ferreira, P., Hemerly, A., de Almeida Engler, J., Bergounioux, C., Burssens, S., Van Montagu, M., Engler, G., and Inzé, D. (1994a). Three discrete classes of Arabidopsis cyclins are expressed during different intervals of the cell cycle. Proc. Natl. Acad. Sci. USA 91, 11313–11317.[Abstract/Free Full Text]
Ferreira, P.C.G., Hemerly, A.S., de Almeida Engler, J., Van Montagu, M., Engler, G., and Inzé, D. (1994b). Developmental expression of the Arabidopsis cyclin gene cyc1At. Plant Cell 6, 1763–1774.[Abstract/Free Full Text]
Fobert, P.R., Coen, E.S., Murphy, G.J.P., and Doonan, J.H. (1994). Patterns of cell division revealed by transcriptional regulation of genes during the cell cycle in plants. EMBO J. 13, 616–624.[Web of Science][Medline]
Genschik, P., Criqui, M.C., Parmentier, Y., Derevier, A., and Fleck, J. (1998). Cell cycle-dependent proteolysis in plants: Identification of the destruction box pathway and metaphase arrest produced by the protease inhibitor MG132. Plant Cell 10, 2063–2075.[Abstract/Free Full Text]
Gray, W.M., del Pozo, J.C., Walker, L., Hobbie, L., Risseeuw, E., Banks, T., Crosby, W.L., Yang, M., Ma, H., and Estelle, M. (1999). Identification of an SCF ubiquitin-ligase complex required for auxin response in Arabidopsis thaliana. Genes Dev. 13, 1678–1691.[Abstract/Free Full Text]
Hemerly, A.S., Ferreira, P., de Almeida Engler, J., Van Montagu, M., Engler, G., and Inzé, D. (1993). cdc2a expression in Arabidopsis is linked with competence for cell division. Plant Cell 5, 1711–1723.[Abstract]
John, P., Mews, M., and Moore, R. (2001). Cyclin/Cdk complexes: Their involvement in cell cycle progression and mitotic division. Protoplasma 216, 119–142.[Medline]
Joubès, J., Chevalier, C., Dudits, D., Heberle-Bors, E., Inzé, D., Umeda, M., and Renaudin, J.-P. (2000). CDK-related protein kinases in plants. Plant Mol. Biol. 43, 607–620.[CrossRef][Web of Science][Medline]
Kosugi, S., and Ohashi, Y. (2002). Interaction of the Arabidopsis E2F and DP proteins confers their concomitant nuclear translocation and transactivation. Plant Physiol. 128, 833–843.[Abstract/Free Full Text]
Laskowski, M.J., Williams, M.E., Nusbaum, H.C., and Sussex, I.M. (1995). Formation of lateral root meristems is a two-stage process. Development 121, 3303–3310.[Abstract]
Magyar, Z., Atanassova, A., De Veylder, L., Rombauts, S., and Inzé, D. (2000). Characterization of two distinct DP-related genes from Arabidopsis thaliana. FEBS Lett. 486, 79–87.[CrossRef][Web of Science][Medline]
Malamy, J.E., and Benfey, P.N. (1997). Organization and cell differentiation in lateral roots of Arabidopsis thaliana. Development 124, 33–44.[Abstract]
Malamy, J.E., and Ryan, K.S. (2001). Environmental regulation of lateral root initiation in Arabidopsis. Plant Physiol. 127, 899–909.[Abstract/Free Full Text]
Martinez, M.C., Jørgensen, J.-E., Lawton, M.A., Lamb, C.J., and Doerner, P.W. (1992). Spatial pattern of cdc2 expression in relation to meristem activity and cell proliferation during plant development. Proc. Natl. Acad. Sci. USA 89, 7360–7364.[Abstract/Free Full Text]
Meijer, M., and Murray, J.A.H. (2000). The role and regulation of D-type cyclins in the plant cell cycle. Plant Mol. Biol. 43, 621–633.[CrossRef][Web of Science][Medline]
Menges, M., and Murray, J.A.H. (2002). Synchronous Arabidopsis suspension cultures for analysis of cell-cycle gene activity. Plant J. 20, 203–212.
Mironov, V., De Veylder, L., Van Montagu, M., and Inzé, D. (1999). Cyclin-dependent kinases and cell division in higher plants: The nexus. Plant Cell 11, 509–521.[Free Full Text]
Müller, A., Hillebrand, H., and Weiler, E.W. (1998). Indole-3-acetic acid is synthesized from L-tryptophan in roots of Arabidopsis thaliana. Planta 206, 362–369.[CrossRef][Web of Science][Medline]
Murashige, T., and Skoog, F. (1962). A revised medium for rapid growth and bio assays with tobacco tissue cultures. Physiol. Plant. 15, 473–497.[CrossRef]
Nougarede, A., and Rondet, P. (1983). Bases cytophysiologiques de l'induction rhizogène en réponse à un traitement auxinique dans l'épicotyle du Pois nain. Ann. Sci. Nat. Bot. 5, 121–149.
Pagano, M., Tam, S.W., Theodoras, A.M., Beer-Romero, P., Del Sal, G., Chau, V., Yew, P.R., Draetta, G.F., and Rolfe, M. (1995). Role of the ubiquitin-proteasome pathway in regulating abundance of the cyclin-dependent kinase inhibitor p27. Science 269, 682–685.[Abstract/Free Full Text]
Planchais, S., Glab, N., Inzé, D., and Bergounioux, C. (2000). Chemical inhibitors: A tool for plant cell cycle studies. FEBS Lett. 476, 78–83.[CrossRef][Web of Science][Medline]
Renaudin, J.P., Savouré, A., Philippe, H., Van Montagu, M., Inzé, D., and Rouzé, P. (1998). Characterization and classification of plant cyclin sequences related to A- and B-type cyclins. In Plant Cell Division, Portland Press Research Monograph X, D. Francis, D. Dudits, and D. Inzé, eds (London: Portland Press), pp. 67–98.
Richard, C., Granier, C., Inzé, D., and De Veylder, L. (2001). Analysis of cell division parameters and cell cycle gene expression during the cultivation of Arabidopsis thaliana cell suspensions. J. Exp. Bot. 52, 1625–1633.[Abstract/Free Full Text]
Richard, C., Lescot, M., Inzé, D., and De Veylder, L. (2002). Effect of auxin, cytokinin, and sucrose on cell cycle gene expression in Arabidopsis thaliana cell suspension cultures. Plant Tissue Organ Cult. 69, 167–176.[CrossRef]
Sabatini, S., Beis, D., Wolkenfelt, H., Murfett, J., Guilfoyle, T., Malamy, J., Benfey, P., Leyser, O., Bechtold, N., Weisbeek, P., and Scheres, B. (1999). An auxin-dependent distal organizer of pattern and polarity in the Arabidopsis root. Cell 99, 463–472.[CrossRef][Web of Science][Medline]
Shaul, O., Mironov, V., Burssens, S., Van Montagu, M., and Inzé, D. (1996). Two Arabidopsis cyclin promoters mediate distinctive transcriptional oscillation in synchronized tobacco BY-2 cells. Proc. Natl. Acad. Sci. USA 93, 4868–4872.[Abstract/Free Full Text]
Soni, R., Carmichael, J.P., Shah, Z.H., and Murray, J.A.H. (1995). A family of cyclin D homologs from plants differentially controlled by growth regulators and containing the conserved retinoblastoma protein interaction motif. Plant Cell 7, 85–103.[Abstract]
Stals, H., and Inzé, D. (2001). When plant cells decide to divide. Trends Plant Sci. 6, 359–364.[CrossRef][Web of Science][Medline]
Taylor, B.H., and Scheuring, C.F. (1994). A molecular marker for lateral root initiation: The RSI-1 gene of tomato (Lycopersicon esculentum Mill) is activated in early lateral root primordia. Mol. Gen. Genet. 243, 148–157.[Medline]
Ulmasov, T., Murfett, J., Hagen, G., and Guilfoyle, T.J. (1997). Aux/IAA proteins repress expression of reporter genes containing natural and highly active synthetic auxin response elements. Plant Cell 9, 1963–1971.[Abstract]
Valvekens, D., Van Montagu, M., and Van Lijsebettens, M. (1988). Agrobacterium tumefaciens-mediated transformation of Arabidopsis thaliana root explants by using kanamycin selection. Proc. Natl. Acad. Sci. USA 85, 5536–5540.[Abstract/Free Full Text]
Wang, H., Fowke, L., and Crosby, W. (1997). A plant cyclin-dependent kinase inhibitor gene. Nature 386, 451–452.[CrossRef][Medline]
Wang, H., Qi, Q., Schorr, P., Cutler, A.J., Crosby, W.L., and Fowke, L.C. (1998). ICK1, a cyclin-dependent protein kinase inhibitor from Arabidopsis thaliana interacts with both Cdc2a and CycD3, and its expression is induced by abscisic acid. Plant J. 15, 501–510.[CrossRef][Web of Science][Medline]
Wang, H., Zhou, Y., Gilmer, S., Whitwill, S., and Fowke, L.C. (2000). Expression of the plant cyclin-dependent kinase inhibitor ICK1 affects cell division, plant growth and morphology. Plant J. 24, 613–623.[CrossRef][Web of Science][Medline]
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The MYB96 Transcription Factor Mediates Abscisic Acid Signaling during Drought Stress Response in Arabidopsis
Plant Physiology,
September 1, 2009;
151(1):
275 - 289.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Ishida, S. Fujiwara, K. Miura, N. Stacey, M. Yoshimura, K. Schneider, S. Adachi, K. Minamisawa, M. Umeda, and K. Sugimoto
SUMO E3 Ligase HIGH PLOIDY2 Regulates Endocycle Onset and Meristem Maintenance in Arabidopsis
PLANT CELL,
August 1, 2009;
21(8):
2284 - 2297.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. K. Mandadi, A. Misra, S. Ren, and T. D. McKnight
BT2, a BTB Protein, Mediates Multiple Responses to Nutrients, Stresses, and Hormones in Arabidopsis
Plant Physiology,
August 1, 2009;
150(4):
1930 - 1939.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. C. Strader and B. Bartel
The Arabidopsis PLEIOTROPIC DRUG RESISTANCE8/ABCG36 ATP Binding Cassette Transporter Modulates Sensitivity to the Auxin Precursor Indole-3-Butyric Acid
PLANT CELL,
July 1, 2009;
21(7):
1992 - 2007.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Sun, Y. Xu, S. Ye, H. Jiang, Q. Chen, F. Liu, W. Zhou, R. Chen, X. Li, O. Tietz, et al.
Arabidopsis ASA1 Is Important for Jasmonate-Mediated Regulation of Auxin Biosynthesis and Transport during Lateral Root Formation
PLANT CELL,
May 1, 2009;
21(5):
1495 - 1511.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. G. Dubrovsky, A. Soukup, S. Napsucialy-Mendivil, Z. Jeknic, and M. G. Ivanchenko
The lateral root initiation index: an integrative measure of primordium formation
Ann. Bot.,
March 1, 2009;
103(5):
807 - 817.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. A. Contreras-Cornejo, L. Macias-Rodriguez, C. Cortes-Penagos, and J. Lopez-Bucio
Trichoderma virens, a Plant Beneficial Fungus, Enhances Biomass Production and Promotes Lateral Root Growth through an Auxin-Dependent Mechanism in Arabidopsis
Plant Physiology,
March 1, 2009;
149(3):
1579 - 1592.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C.-A. Perez-Torres, J. Lopez-Bucio, A. Cruz-Ramirez, E. Ibarra-Laclette, S. Dharmasiri, M. Estelle, and L. Herrera-Estrella
Phosphate Availability Alters Lateral Root Development in Arabidopsis by Modulating Auxin Sensitivity via a Mechanism Involving the TIR1 Auxin Receptor
PLANT CELL,
December 1, 2008;
20(12):
3258 - 3272.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
I. De Smet, V. Vassileva, B. De Rybel, M. P. Levesque, W. Grunewald, D. Van Damme, G. Van Noorden, M. Naudts, G. Van Isterdael, R. De Clercq, et al.
Receptor-Like Kinase ACR4 Restricts Formative Cell Divisions in the Arabidopsis Root
Science,
October 24, 2008;
322(5901):
594 - 597.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Guo, K. Xia, and Z.-M. Yang
Regulation of tomato lateral root development by carbon monoxide and involvement in auxin and nitric oxide
J. Exp. Bot.,
September 1, 2008;
59(12):
3443 - 3452.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Watanabe, K. Mochida, T. Kato, S. Tabata, N. Yoshimoto, M. Noji, and K. Saito
Comparative Genomics and Reverse Genetics Analysis Reveal Indispensable Functions of the Serine Acetyltransferase Gene Family in Arabidopsis
PLANT CELL,
September 1, 2008;
20(9):
2484 - 2496.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
W. Grunewald, M. Karimi, K. Wieczorek, E. Van de Cappelle, E. Wischnitzki, F. Grundler, D. Inze, T. Beeckman, and G. Gheysen
A Role for AtWRKY23 in Feeding Site Establishment of Plant-Parasitic Nematodes
Plant Physiology,
September 1, 2008;
148(1):
358 - 368.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
F. Q. Fu, W. H. Mao, K. Shi, Y. H. Zhou, T. Asami, and J. Q. Yu
A role of brassinosteroids in early fruit development in cucumber
J. Exp. Bot.,
June 1, 2008;
59(9):
2299 - 2308.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Tapia-Lopez, B. Garcia-Ponce, J. G. Dubrovsky, A. Garay-Arroyo, R. V. Perez-Ruiz, S.-H. Kim, F. Acevedo, S. Pelaz, and E. R. Alvarez-Buylla
An AGAMOUS-Related MADS-Box Gene, XAL1 (AGL12), Regulates Root Meristem Cell Proliferation and Flowering Transition in Arabidopsis
Plant Physiology,
March 1, 2008;
146(3):
1182 - 1192.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Lucas, C. Godin, C. Jay-Allemand, and L. Laplaze
Auxin fluxes in the root apex co-regulate gravitropism and lateral root initiation
J. Exp. Bot.,
January 1, 2008;
59(1):
55 - 66.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. U. Andersen, S. Buechel, Z. Zhao, K. Ljung, O. Novak, W. Busch, C. Schuster, and J. U. Lohmann
Requirement of B2-Type Cyclin-Dependent Kinases for Meristem Integrity in Arabidopsis thaliana
PLANT CELL,
January 1, 2008;
20(1):
88 - 100.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. Parizot, L. Laplaze, L. Ricaud, E. Boucheron-Dubuisson, V. Bayle, M. Bonke, I. De Smet, S. R. Poethig, Y. Helariutta, J. Haseloff, et al.
Diarch Symmetry of the Vascular Bundle in Arabidopsis Root Encompasses the Pericycle and Is Reflected in Distich Lateral Root Initiation
Plant Physiology,
January 1, 2008;
146(1):
140 - 148.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Watanabe, M. Kusano, A. Oikawa, A. Fukushima, M. Noji, and K. Saito
Physiological Roles of the -Substituted Alanine Synthase Gene Family in Arabidopsis
Plant Physiology,
January 1, 2008;
146(1):
310 - 320.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. Laplaze, E. Benkova, I. Casimiro, L. Maes, S. Vanneste, R. Swarup, D. Weijers, V. Calvo, B. Parizot, M. B. Herrera-Rodriguez, et al.
Cytokinins Act Directly on Lateral Root Founder Cells to Inhibit Root Initiation
PLANT CELL,
December 1, 2007;
19(12):
3889 - 3900.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. A. Dong, J. L. Bufford, Y. Oono, K. Church, M. Q. Dau, K. Michels, M. Haughton, and G. Tallman
Heat Suppresses Activation of an Auxin-Responsive Promoter in Cultured Guard Cell Protoplasts of Tree Tobacco
Plant Physiology,
October 1, 2007;
145(2):
367 - 377.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. P. Vidaurre, S. Ploense, N. T. Krogan, and T. Berleth
AMP1 and MP antagonistically regulate embryo and meristem development in Arabidopsis
Development,
July 15, 2007;
134(14):
2561 - 2567.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Hirota, T. Kato, H. Fukaki, M. Aida, and M. Tasaka
The Auxin-Regulated AP2/EREBP Gene PUCHI Is Required for Morphogenesis in the Early Lateral Root Primordium of Arabidopsis
PLANT CELL,
July 1, 2007;
19(7):
2156 - 2168.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Trusov, J. E. Rookes, K. Tilbrook, D. Chakravorty, M. G. Mason, D. Anderson, J.-G. Chen, A. M. Jones, and J. R. Botella
Heterotrimeric G Protein {gamma} Subunits Provide Functional Selectivity in G{beta}{gamma} Dimer Signaling in Arabidopsis
PLANT CELL,
April 1, 2007;
19(4):
1235 - 1250.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
I. De Smet, T. Tetsumura, B. De Rybel, N. F. d. Frey, L. Laplaze, I. Casimiro, R. Swarup, M. Naudts, S. Vanneste, D. Audenaert, et al.
Auxin-dependent regulation of lateral root positioning in the basal meristem of Arabidopsis
Development,
February 15, 2007;
134(4):
681 - 690.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. Fleury, K. Himanen, G. Cnops, H. Nelissen, T. M. Boccardi, S. Maere, G. T.S. Beemster, P. Neyt, S. Anami, P. Robles, et al.
The Arabidopsis thaliana Homolog of Yeast BRE1 Has a Function in Cell Cycle Regulation during Early Leaf and Root Growth
PLANT CELL,
February 1, 2007;
19(2):
417 - 432.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Okushima, H. Fukaki, M. Onoda, A. Theologis, and M. Tasaka
ARF7 and ARF19 Regulate Lateral Root Formation via Direct Activation of LBD/ASL Genes in Arabidopsis
PLANT CELL,
January 1, 2007;
19(1):
118 - 130.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Yoshida, N. Imaizumi, S. Kaneko, Y. Kawagoe, A. Tagiri, H. Tanaka, K. Nishitani, and K. Komae
Carbohydrate-Binding Module of a Rice Endo-{beta}-1,4-glycanase, OsCel9A, Expressed in Auxin-Induced Lateral Root Primordia, is Post-Translationally Truncated
Plant Cell Physiol.,
November 1, 2006;
47(11):
1555 - 1571.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. M. Barroco, A. Peres, A.-M. Droual, L. De Veylder, L. S. L. Nguyen, J. De Wolf, V. Mironov, R. Peerbolte, G. T.S. Beemster, D. Inze, et al.
The Cyclin-Dependent Kinase Inhibitor Orysa;KRP1 Plays an Important Role in Seed Development of Rice
Plant Physiology,
November 1, 2006;
142(3):
1053 - 1064.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Yoshizumi, Y. Tsumoto, T. Takiguchi, N. Nagata, Y. Y. Yamamoto, M. Kawashima, T. Ichikawa, M. Nakazawa, N. Yamamoto, and M. Matsui
INCREASED LEVEL OF POLYPLOIDY1, a Conserved Repressor of CYCLINA2 Transcription, Controls Endoreduplication in Arabidopsis
PLANT CELL,
October 1, 2006;
18(10):
2452 - 2468.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. C. del Pozo, S. Diaz-Trivino, N. Cisneros, and C. Gutierrez
The Balance between Cell Division and Endoreplication Depends on E2FC-DPB, Transcription Factors Regulated by the Ubiquitin-SCFSKP2A Pathway in Arabidopsis
PLANT CELL,
September 1, 2006;
18(9):
2224 - 2235.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
X. Cai, E. J. Davis, J. Ballif, M. Liang, E. Bushman, V. Haroldsen, J. Torabinejad, and Y. Wu
Mutant identification and characterization of the laccase gene family in Arabidopsis
J. Exp. Bot.,
August 1, 2006;
57(11):
2563 - 2569.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
X. Li, X. Mo, H. Shou, and P. Wu
Cytokinin-Mediated Cell Cycling Arrest of Pericycle Founder Cells in Lateral Root Initiation of Arabidopsis
Plant Cell Physiol.,
August 1, 2006;
47(8):
1112 - 1123.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. J. Rose, X.-D. Wang, K. E. Nolan, and B. G. Rolfe
Root meristems in Medicago truncatula tissue culture arise from vascular-derived procambial-like cells in a process regulated by ethylene
J. Exp. Bot.,
July 1, 2006;
57(10):
2227 - 2235.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J.-G. Chen, Y. Gao, and A. M. Jones
Differential Roles of Arabidopsis Heterotrimeric G-Protein Subunits in Modulating Cell Division in Roots
Plant Physiology,
July 1, 2006;
141(3):
887 - 897.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. Bisbis, F. Delmas, J. Joubes, A. Sicard, M. Hernould, D. Inze, A. Mouras, and C. Chevalier
Cyclin-dependent Kinase (CDK) Inhibitors Regulate the CDK-Cyclin Complex Activities in Endoreduplicating Cells of Developing Tomato Fruit
J. Biol. Chem.,
March 17, 2006;
281(11):
7374 - 7383.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Correa-Aragunde, M. Graziano, C. Chevalier, and L. Lamattina
Nitric oxide modulates the expression of cell cycle regulatory genes during lateral root formation in tomato
J. Exp. Bot.,
February 1, 2006;
57(3):
581 - 588.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. K. Zhiponova, A. Pettko-Szandtner, E. Stelkovics, Z. Neer, S. Bottka, T. Krenacs, D. Dudits, A. Feher, and L. Szilak
Mitosis-Specific Promoter of the Alfalfa Cyclin-Dependent Kinase Gene (Medsa;CDKB2;1) Is Activated by Wounding and Ethylene in a Non-Cell Division-Dependent Manner
Plant Physiology,
February 1, 2006;
140(2):
693 - 703.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Konishi and M. Sugiyama
A Novel Plant-Specific Family Gene, ROOT PRIMORDIUM DEFECTIVE 1, Is Required for the Maintenance of Active Cell Proliferation
Plant Physiology,
February 1, 2006;
140(2):
591 - 602.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. C. Coates, L. Laplaze, and J. Haseloff
Armadillo-related proteins promote lateral root development in Arabidopsis
PNAS,
January 31, 2006;
103(5):
1621 - 1626.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
X. Wang, Y. Xu, Y. Han, S. Bao, J. Du, M. Yuan, Z. Xu, and K. Chong
Overexpression of RAN1 in Rice and Arabidopsis Alters Primordial Meristem, Mitotic Progress, and Sensitivity to Auxin
Plant Physiology,
January 1, 2006;
140(1):
91 - 101.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Verkest, C. Weinl, D. Inze, L. De Veylder, and A. Schnittger
Switching the Cell Cycle. Kip-Related Proteins in Plant Cell Cycle Control
Plant Physiology,
November 1, 2005;
139(3):
1099 - 1106.
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Vanneste, B. De Rybel, G. T.S. Beemster, K. Ljung, I. De Smet, G. Van Isterdael, M. Naudts, R. Iida, W. Gruissem, M. Tasaka, et al.
Cell Cycle Progression in the Pericycle Is Not Sufficient for SOLITARY ROOT/IAA14-Mediated Lateral Root Initiation in Arabidopsis thaliana
PLANT CELL,
November 1, 2005;
17(11):
3035 - 3050.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Yamazoe, K.-i. Hayashi, S. Kepinski, O. Leyser, and H. Nozaki
Characterization of Terfestatin A, a New Specific Inhibitor for Auxin Signaling
Plant Physiology,
October 1, 2005;
139(2):
779 - 789.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. Nacry, G. Canivenc, B. Muller, A. Azmi, H. Van Onckelen, M. Rossignol, and P. Doumas
A Role for Auxin Redistribution in the Responses of the Root System Architecture to Phosphate Starvation in Arabidopsis
Plant Physiology,
August 1, 2005;
138(4):
2061 - 2074.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. A. Tomilov, N. B. Tomilova, I. Abdallah, and J. I. Yoder
Localized Hormone Fluxes and Early Haustorium Development in the Hemiparasitic Plant Triphysaria versicolor
Plant Physiology,
July 1, 2005;
138(3):
1469 - 1480.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Vissenberg, M. Oyama, Y. Osato, R. Yokoyama, J.-P. Verbelen, and K. Nishitani
Differential Expression of AtXTH17, AtXTH18, AtXTH19 and AtXTH20 Genes in Arabidopsis Roots. Physiological Roles in Specification in Cell Wall Construction
Plant Cell Physiol.,
January 15, 2005;
46(1):
192 - 200.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. M. Zgurski, R. Sharma, D. A. Bolokoski, and E. A. Schultz
Asymmetric Auxin Response Precedes Asymmetric Growth and Differentiation of asymmetric leaf1 and asymmetric leaf2 Arabidopsis Leaves
PLANT CELL,
January 1, 2005;
17(1):
77 - 91.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Brinker, L. van Zyl, W. Liu, D. Craig, R. R. Sederoff, D. H. Clapham, and S. von Arnold
Microarray Analyses of Gene Expression during Adventitious Root Development in Pinus contorta
Plant Physiology,
July 1, 2004;
135(3):
1526 - 1539.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Himanen, M. Vuylsteke, S. Vanneste, S. Vercruysse, E. Boucheron, P. Alard, D. Chriqui, M. Van Montagu, D. Inze, and T. Beeckman
Transcript profiling of early lateral root initiation
PNAS,
April 6, 2004;
101(14):
5146 - 5151.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Stevens, M. Grelon, D. Vezon, J. Oh, P. Meyer, C. Perennes, S. Domenichini, and C. Bergounioux
A CDC45 Homolog in Arabidopsis Is Essential for Meiosis, as Shown by RNA Interference-Induced Gene Silencing
PLANT CELL,
January 1, 2004;
16(1):
99 - 113.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Himanen, C. Reuzeau, T. Beeckman, S. Melzer, O. Grandjean, L. Corben, and D. Inze
The Arabidopsis Locus RCB Mediates Upstream Regulation of Mitotic Gene Expression
Plant Physiology,
December 1, 2003;
133(4):
1862 - 1872.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
P. Campanoni, B. Blasius, and P. Nick
Auxin Transport Synchronizes the Pattern of Cell Division in a Tobacco Cell Line
Plant Physiology,
November 1, 2003;
133(3):
1251 - 1260.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Oono, C. Ooura, A. Rahman, E. T. Aspuria, K.-i. Hayashi, A. Tanaka, and H. Uchimiya
p-Chlorophenoxyisobutyric Acid Impairs Auxin Response in Arabidopsis Root
Plant Physiology,
November 1, 2003;
133(3):
1135 - 1147.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H.-H. Woo, K. F. Faull, A. M. Hirsch, and M. C. Hawes
Altered Life Cycle in Arabidopsis Plants Expressing PsUGT1, a UDP-Glucuronosyltransferase-Encoding Gene from Pea
Plant Physiology,
October 1, 2003;
133(2):
538 - 548.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Kono, C. Umeda-Hara, J. Lee, M. Ito, H. Uchimiya, and M. Umeda
Arabidopsis D-Type Cyclin CYCD4;1 Is a Novel Cyclin Partner of B2-Type Cyclin-Dependent Kinase
Plant Physiology,
July 1, 2003;
132(3):
1315 - 1321.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
F. Roudier, E. Fedorova, M. Lebris, P. Lecomte, J. Gyorgyey, D. Vaubert, G. Horvath, P. Abad, A. Kondorosi, and E. Kondorosi
The Medicago Species A2-Type Cyclin Is Auxin Regulated and Involved in Meristem Formation But Dispensable for Endoreduplication-Associated Developmental Programs
Plant Physiology,
March 1, 2003;
131(3):
1091 - 1103.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Ullah, J.-G. Chen, B. Temple, D. C. Boyes, J. M. Alonso, K. R. Davis, J. R. Ecker, and A. M. Jones
The {beta}-Subunit of the Arabidopsis G Protein Negatively Regulates Auxin-Induced Cell Division and Affects Multiple Developmental Processes
PLANT CELL,
February 1, 2003;
15(2):
393 - 409.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
TOP
Abstract
INTRODUCTION