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© 2004 American Society of Plant Biologists The xipotl Mutant of Arabidopsis Reveals a Critical Role for Phospholipid Metabolism in Root System Development and Epidermal Cell Integrity
a Departamento de Ingeniería Genética Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional Unidad Irapuato, Apartado Postal 629 36500 Irapuato, Guanajuato, Mexico 2 To whom correspondence should be addressed. E-mail lherrera{at}ira.cinvestav.mx; fax 462-624-58-46.
Phosphocholine (PCho) is an essential metabolite for plant development because it is the precursor for the biosynthesis of phosphatidylcholine, which is the major lipid component in plant cell membranes. The main step in PCho biosynthesis in Arabidopsis thaliana is the triple, sequential N-methylation of phosphoethanolamine, catalyzed by S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferase (PEAMT). In screenings performed to isolate Arabidopsis mutants with altered root system architecture, a T-DNA mutagenized line showing remarkable alterations in root development was isolated. At the seedling stage, the mutant phenotype is characterized by a short primary root, a high number of lateral roots, and short epidermal cells with aberrant morphology. Genetic and biochemical characterization of this mutant showed that the T-DNA was inserted at the At3g18000 locus (XIPOTL1), which encodes PEAMT (XIPOTL1). Further analyses revealed that inhibition of PCho biosynthesis in xpl1 mutants not only alters several root developmental traits but also induces cell death in root epidermal cells. Epidermal cell death could be reversed by phosphatidic acid treatment. Taken together, our results suggest that molecules produced downstream of the PCho biosynthesis pathway play key roles in root development and act as signals for cell integrity.
Phosphatidylcholine (PtdCho) is a major phospholipid present in mammalian, plant, yeast, and some prokaryote cell membranes. PtdCho has been demonstrated to play critical roles both as a structural component in cell membranes and in cellular signaling. In mammalian cells, the perturbation of PtdCho homeostasis caused by mutations, inhibitors, or nutrient deficiency retards cell growth and leads to cell death (Cui and Vance, 1996  ; Cui et al., 1996; Yen et al., 1999; Ramos et al., 2000). In plants, PtdCho is the most abundant phospholipid in cell membranes, accounting for up to 60% of total membrane lipids (Datko and Mudd, 1988a; Prud'homme and Moore, 1992; Moreau et al., 1998). It has been shown that the main biosynthetic pathway for PtdCho production in plants is the CDP-choline pathway, which is also found in yeast and other eukaryotes (Datko and Mudd, 1988b; Bolognese and McGraw, 2000). This pathway depends on phosphocholine (PCho) acting as a precursor in the synthesis of PtdCho. Plants produce PCho via a triple, sequential N-methylation of phosphoethanolamine (PEA), reactions performed by a single enzyme, S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferase (PEAMT) (Datko and Mudd, 1988b; Munnik et al., 1998; Bolognese and McGraw, 2000; McNeil et al., 2000; Nuccio et al., 2000; Smith et al., 2000). Three loci encoding putative PEAMTs (At1g48600, At1g73600, and At3g18000) have been identified in the Arabidopsis thaliana genome database. Complementation studies of the Saccharomyces cerevisiae opi3 mutant affected in PtdCho synthesis demonstrated that at least one of these loci, At3g18000 (XIPOTL1), indeed encodes an enzyme with PEAMT activity (McGraw and Henry, 1989; Bolognese and McGraw, 2000). Some authors suggest that PCho could be synthesized via an untested metabolic step in Arabidopsis: the conversion of choline (Cho) to PCho, catalyzed by a Cho kinase (Kinney and Moore, 1987; Bolognese and McGraw, 2000). Silencing of the PEAMT gene family in transgenic Arabidopsis lines was reported to cause temperature-sensitive male sterility, decreased Cho production, and hypersensitivity to salt stress (Mou et al., 2002).
PtdCho is not only a structural component of plant membranes, it can also be converted into phosphatidic acid (PA) and free Cho by phospholipase D (PLD). This metabolic step could become increasingly important considering that recent studies using plant cell cultures suggest that PA is a new signal molecule acting as a secondary messenger, which plays diverse roles in plant development (Munnik et al., 1998
Isolation of an Arabidopsis Mutant Affected in Root Development Screening of Arabidopsis plants from a T-DNA–mutagenized collection resulted in the isolation of several mutant seedlings with altered root architecture. Among them, line 287 showed a remarkable phenotype in the root system (Figure 1). This line showed evident differences in root system architecture at both early (8 d after germination [dag]) and late (40 dag) developmental stages (Figure 1). At early stages of development, the primary root of line 287 was approximately four times shorter than in wild-type plants and had longer lateral roots than the wild type (Figure 1A). Line 287 is fully fertile and at a late developmental stage, no major developmental changes in the aerial part of the plant were observed, except for a slight delay in the growth of some floral stems (Figure 1B). However, the root system of adult plants of line 287 was found to be significantly shorter (3 cm in length) than in wild-type plants (7 cm in length) (Figure 1C). Crosses with wild-type plants showed that the mutation affecting line 287 was recessive, with a segregation pattern corresponding to a single affected gene (data not shown). As we will describe below, line 287 was named xipotl, a Nahuatl term that means swelling or tumefaction, because of the swelling observed in epidermal cells of this mutant.
xipotl Is an Insertional Mutant in the At3g18000 Locus To determine whether the T-DNA insertion cosegregated with the observed xipotl phenotype, 100 mutant seedlings from the F2 progeny of a cross between xipotl and the wild type were tested for the presence of the T-DNA encoded kanamycin resistance gene. Growth in kanamycin-containing media and PCR analysis showed that in all tested mutant seedlings the resistance gene was present, indicating that the T-DNA cosegregated with the mutant phenotype (data not shown). Using the thermal asymmetric interlaced-PCR technique, we determined that the T-DNA present in the xipotl mutant was inserted in exon 7 of the At3g18000 locus that encodes for XIPOTL1. A search in the Salk T-DNA insertion collection identified a line (mutant S_036291) with an insertion in exon 10 of XPL1 (Figure 2A). Phenotypic analysis showed that line S-036291 presents a similar phenotype to that observed for xipotl in terms of reduced primary root length, increased lateral root formation, and reduced number of root hairs. To determine whether the T-DNA insertion in XPL1 in xipotl and line S_036291 was responsible for the observed mutant phenotype, we performed reciprocal crosses between the two mutants. Analysis of more than 30 seedlings from each of the crosses demonstrated that all F1 plants showed the xipotl phenotype, confirming that the gene affected in both mutants is the same (Figure 2B). PCR-based genotyping of the F2 progeny of a cross between xipotl and the wild type using oligonucleotides specific for XPL1 and a primer specific for the right or left border of the T-DNA showed that all mutant seedlings were homozygous for the T-DNA insertion in XPL1, whereas wild-type seedlings were either heterozygous for the T-DNA insertion or lacked the T-DNA (data not shown).
To determine if XPL1 expression was affected in xpl1 and S_036291 mutants, total RNA from 10-d-old mutant and wild-type plants was extracted, and gene-specific primers were designed for transcript detection by RT-PCR. Transcripts of XPL1 were not detected in xipotl and S_036291 plants, whereas XPL1 transcription was detected in wild-type plants (Figure 2C). To establish whether XPL1 is expressed in different plant tissues or only in roots, gene-specific primers were designed, total RNA was extracted from rosette leaves, roots, siliques, cauline leaves, and infloresences of wild-type plants, and transcript detection was performed by RT-PCR. Transcripts of XPL1 were detected in all of these tissues (Figure 2D), being apparently less abundant in leaves than in roots, infloresences, and silique tissues.
xipotl Is Affected in Primary Root Elongation and Root Epidermal Cell Development
Microscopic analysis showed that the roots of xipotl had few root hairs and evident abnormalities in epidermal cells. Root hair number in mutant plants was determined to be four times lower in comparison to the wild type (Figure 3C). After a more detailed analysis of xipotl roots, it was observed that even though the root meristematic region appeared relatively normal, it was shorter than in the wild type (Figures 4A and 4E). Moreover, in some regions of the elongation and differentiation zones, the epidermal cells, and probably also cortical and endodermal cells had abnormal morphologies (Figures 4F to 4H), in comparison to those of the control (Figures 4B to 4D). Extreme alterations in root hair formation and development were observed in the differentiation zone, where not only zones lacking root hairs or having short root hairs were found but also globular shaped and collapsed cells were observed (Figure 4H).
The short primary root phenotype observed in xipotl could be a result of reduced cell division or a reduction in cell size. Because the primary root meristem appears normal, we analyzed whether cell elongation was affected in xipotl by measuring the epidermal cell size in three root regions: the elongation zone and the proximal and distal regions of the differentiation zone of the primary root in wild-type and mutant plants (Figure 4I). These measurements show that, in the three root regions, the cells of the xipotl mutant are on average 50% shorter than those of the wild type (Figures 4J and 4K).
Rescue of the Mutant Phenotype by PCho and Cho
It has been reported that the salt hypersensitivity of PEAMT silenced lines is reversed by the addition of Cho (Mou et al., 2002 ). To test whether Cho can also suppress the xipotl phenotype, we sowed mutant and wild-type seeds on complete solid MS media supplemented with Cho. It was found that the mutant phenotype was also completely restored by adding Cho to the media (Figure 5C; data not shown). Taken together, these results show that a reduction in the synthesis of PCho and/or other compounds derived from it, such as PtdCho, impairs normal root development. The finding that Cho also restores normal root development in the xipotl1 mutant suggests that Cho can be converted into PCho in planta via a Cho phosphorylation reaction.
Inhibition of PCho Biosynthesis Induces Death in Epidermal and Root Hair Cells Microscopic analysis revealed that in the roots of 8-d-old wild-type seedlings, all cells at the meristematic, elongation, and distinct differentiation zones, with the exception of the xylem, were alive because FDA was actively converted into fluorescein producing a green color, whereas PI stained only the cell walls, and no staining was observed inside the cells (Figures 6A to 6C). By contrast, numerous epidermal and cortical dead cells, as evidenced by PI staining inside the cell and lacking green fluorescence, were observed in the meristem and elongation zones of xipotl roots (Figures 6D and 6E). Major damage was observed in certain segments along the differentiation zone, where the nuclei of most of the globular-shaped cells were stained red, and no FDA staining was observed (Figure 6F).
To confirm these results, we stained wild-type and mutant seedlings with Evans blue. This dye reveals cell death because of its ability to enter only those cells with a completely permeable plasma membrane (Mergemann and Sauter, 2000 ). This analysis revealed the absence of stained cells in the wild-type roots (Figure 6G). Conversely, we found large patches of stained cells in the elongation zone of the mutant plant roots (Figure 6H), and along the differentiation zone we observed that most of the globular-shaped cells were dead (Figure 6I). Importantly, the cell death patterns revealed by Evans blue and the double fluorescent staining were in close agreement. Because addition of PCho restores normal root growth in xipotl, we tested whether this treatment also eliminates the abnormal cell death observed in this mutant. Staining with Evans blue showed that addition of exogenous PCho completely eliminates cell death concomitant with the restoration of normal morphology of all cell types in the xipotl root (Figures 6J to 6L). These results confirm that a reduction in the synthesis of PCho, or a compound derived from its metabolism, triggers cell death in some root cell layers.
PA Reverts Cell Death in the Mutant Phenotype
Previous studies established that PLD has a unique ability to transfer the phosphatidyl group of phospholipids to a primary alcohol (1-butanol) rather than water, producing phosphatidyl alcohol and inhibiting the production of PA (Potocky et al., 2003 To further explore the possibility that mutations in XPL1 could reduce PA production and that this reduction might be responsible for some of the phenotypic alterations in xipotl, we tested the effect of different concentrations of exogenous PA on the growth, morphology, and cell death of xipotl seedlings. With this aim in mind, control and mutant seeds were germinated and grown in solid media in the presence of PA and stained with PI or Evans blue. In contrast with what was observed for mutant plants grown in solid media lacking PA, which showed the cell death pattern described before (Figures 7A to 7F), those grown in media with 28 µM PA showed a decrease in cell death and morphological cell abnormalities (Figures 7G to 7L). Treatments with 280 µM PA led to a total recovery of the cell death phenotype and a complete disappearance of globular-shaped epidermal cells (Figures 7M to 7R). However, PA treatment did not restore normal primary root growth or root hair formation. In wild-type plants grown on 28 µM PA, the root phenotype was normal except that root hairs were shorter than those of untreated plants; treatment with 280 µM PA further inhibited root hair and primary root elongation compared with that of the untreated control (data not shown). These results show that treatment with PA can alleviate cell death and some morphological abnormalities observed in the epidermal cells of xipotl and that high concentrations of PA can inhibit root growth and epidermal cell differentiation in wild-type Arabidopsis plants.
xipotl Plants Have a Significant Decrease in PtdCho Content To determine whether mutations in XPL1 cause a reduction in the biosynthesis of PCho, PtdCho, and Cho, we measured the total content of these molecules in the root and leaves of xipotl seedlings. When PCho and Cho were quantified, we found a consistent, albeit statistically nonsignificant, decrease of between 5 and 7% in the content of these two compounds in leaves and roots of xipotl compared with that present in wild-type plants (Table 1). Moreover, when the content of PtdCho in roots and leaves of mutant and wild-type plants was determined, significantly lower levels of PtdCho were detected in xipotl tissues (Table 1). Roots of xpl1 plants showed an  23% decrease in PtdCho content in comparison with those of wild-type plants, whereas the difference in leaves was 18%. Although the contribution of XPL1 for the biosynthesis of PtdCho is significant in root and aerial tissues, the reduction in the synthesis of PtdCho in xpl1 has an evident effect on root but not aerial tissue development. This suggests that the other members of the PEAMT gene family play a more important role in the synthesis of PCho and PtdCho in aerial tissues than XPL1. This is consistent with the differential expression shown by the three PEAMT genes revealed by microarray experiments (L. Nussaume, L. Herrera-Estrella, and K.G. Raghothama, unpublished data). However, to demonstrate this statement, detailed studies of the expression of each of the members of the PEAMT gene family are needed.
XPL1-Specific Expression Revealed by the Whole Mount in Situ Hybridization Technique Because the defects observed in xipotl mainly affect the elongation and differentiation zones of the root, it was important to determine whether XPL1 transcription was restricted to a specific region or cell layer in Arabidopsis roots. Therefore, we analyzed the XPL1 tissue-specific expression pattern by the whole mount RNA in situ hybridization technique in 7-d-old wild-type seedlings. When seedlings hybridized with the sense probe were incubated overnight in the presence of the phosphatase substrate, no hybridization signal was observed (Figures 8A to 8C), whereas in the seedlings hybridized for the same time with the antisense probe, a high level of XPL1 transcripts was detected in the meristem and elongation zones of the root (Figure 8D), and a less intense signal was detected in differentiated epidermal cells (Figure 8E). To observe XPL1 expression in specific cell layers in the root meristem, the time of incubation was reduced to 30 min. We observed that XPL1 transcripts accumulate in the epidermal, cortical, and endodermal cells of the meristematic region and to a lower extent in the elongation zone and columella cells (Figure 8F). No expression was detected in the same cell layers in sense-hybridized seedlings (Figure 8C). Aerial parts of the seedling were devoid of signal except for a weak signal observed at the shoot apical meristem and the hydothodes (data not shown). These results show that XPL1 transcripts are present in high levels in the root regions where cell death and abnormalities are observed.
Important advances have been achieved in the identification of genes involved in the development of the Arabidopsis root system. Genes required for root hair development, auxin signaling, and transcription factors involved in root cell differentiation and maintenance have been isolated (Reire et al., 1994 ; Min Lee and Schiefelbein, 1999; Schiefelbein, 2000; reviewed in López-Bucio et al., 2003). However, many of the signaling pathways regulating root development remain to be identified. Here, we describe the isolation of xipotl, an Arabidopsis mutant affected in root development. xipotl is characterized by a reduced primary root growth and root hair formation and alteration in the morphology of root epidermal cells. The gene responsible for this phenotypic alteration was identified as XPL1 by (1) isolating the border sequences of the T-DNA inserted in the original line in which the xipotl phenotype was identified, (2) the lack of complementation with an independent line that harbors an insertion in XPL1, and (3) the restoration of normal root growth and development by an exogenous supply of PCho, the product of the reaction catalyzed by the enzyme encoded by XPL1. In the Arabidopsis genome database, three loci encoding putative PEAMTs are reported: At1g48600, At1g73600, and At3g18000. If these three loci indeed encode active PEAMTs, the finding that mutations in XPL1 result in a drastic alteration in the development and growth of the root system suggests that the function of the members of this gene family is not completely redundant. RT-PCR analysis showed that XPL1 is expressed in roots, leaves, siliques, and flowers, suggesting that the corresponding gene participates in the synthesis of PtdCho in different organs. However, the finding that mutations in XPL1 only produce a visible phenotype in roots suggests that XPL1 is limiting in providing PCho and/or PCho derived products during root development. Moreover, in situ hybridization experiments showed that in Arabidopsis seedlings XPL1 is preferentially expressed in the meristematic zone and epidermal cells of the Arabidopsis roots, indicating that PtdCho synthesis in these tissues is more severely affected in xpl1. Therefore, we propose that the lack of functional redundancy among the members of the PEAMT gene family is probably because of differential expression of the three PEAMT genes. In agreement with this, microarray experiments showed that XPL1 expression in roots is 3.65 times and 12.84 times higher than in leaves of 5- and 14-d-old plants, respectively, and that the expression of At1g48600 and At1g73600 is higher (10.88 and 6.08 times, respectively) in leaves than that of XPL1 (L. Nussaume, L. Herrera-Estrella, and K.G. Raghothama, unpublished data).
Silencing of the PEAMT gene family in Arabidopsis by sense and antisense expression of PEAMT using the 35S promoter has been reported to result in a phenotype characterized by pale green rosette leaves in juvenile stages, early senescence in the late reproductive stages, short siliques, reduced male fertility, and salt hypersensitivity (Mou et al., 2002
Mou et al. (2002)
Metabolic Implications of xipotl
The finding that not only PCho but also Cho can restore normal root growth and cell morphology in the xipotl mutant coupled with the fact that there are no reported pathways to produce PtdCho directly from Cho suggest that PCho can be produced from Cho by a phosphorylation reaction performed, most probably, by a choline kinase (CK). The presence of genes encoding CKs in plants has been demonstrated by heterologous expression of soybean (Glycine max) CK cDNAs in yeast and Escherichia coli (Monks et al., 1996
Implications of PEAMT in Cell Growth and Cell Death It has been described that in mammalian cells, growth and integrity are directly influenced by changes in cell membrane composition occurring when PtdCho biosynthesis has been perturbed by mutations, inhibition, or nutrient deficiency (Cui et al., 1996 ). We also found that the reduced primary root growth in XPL1 Arabidopsis mutants is related to a 50% reduction in cell elongation. Because PEAMT plays a pivotal role in the PtdCho biosynthetic pathway in plants, reduced root growth and epidermal cell death in xipotl could also be because of perturbation in the synthesis of PtdCho in the root meristem. However, the observation that PA can alleviate cell death suggests that some of cellular phenotypes observed in xipotl are not because of a direct effect in the reduction of PtdCho levels (Figure 9).
Cell death has been classified into physiological cell death and nonphysiological cell death (Vaux and Korsmeyer, 1999
Studies focused on phospholipid signaling show that PtdCho not only plays an important role as an essential component in cell membranes but also as a PLD substrate for the biosynthesis of PA (Exton, 1994
Two pathways have been proposed for the biosynthesis of PA in plants: the PLD pathway and a phospholipase C pathway. The latter involves the conversion of phosphatidylinositolbisphosphate to diacylglycerol by phospholipase C and the conversion of diacylglycerol to PA by diacylglycerol kinase (Munnik, 2001 Our results show that an upstream inhibition of the PtdCho pathway leads to cell death in the Arabidopsis root epidermis (Figure 9). However, to test whether the lack of PtdCho per se was responsible for the observed cell death in xipotl or if this was related to the role of PtdCho as the substrate for PA production, we performed experiments in which PA but not Cho production by PLD was blocked by treatment with 1-butanol. These experiments showed that the inhibition of PA production by PLDs resulted in an arrest of root growth and epidermal cell death, suggesting that the reduction in PA production could be involved in the observed cell death in xipolt. However, we observed that the effects of 1-butanol are more drastic than those observed in the xipotl phenotype.
This difference could be the result of inhibiting PA formation by all PLDs by 1-butanol, and not only that specific for PtdCho or to the effects of 1-butanol on the activation of PLDs that could be involved in microtubule reorganization as recently proposed by Dhonukshe et al. (2003)
GLABRA2 (GL2) is a homeobox transcription factor expressed predominantly in hairless epidermal cell layers and thought to negatively regulate root hair development (Reire et al., 1994
We may conclude that PA is a molecule involved in signal transduction pathways related to cell death and, in accordance with the results of Ohashi et al. (2003)
Plant Growth Conditions Wassilewskija (Ws) and Col 0 are the Arabidopsis thaliana ecotypes of xipotl and S_036291 seedlings, respectively. Mutant and wild-type seeds were surface sterilized with 95% (v/v) ethanol for 5 min and 20% (v/v) bleach for 7 min. After five washes in distilled water, seeds were germinated and grown on agar plates containing complete Murashige and Skoog (solid MS) medium, which depending on the type of experiments, was supplemented with different chemicals. Plates were placed vertically at an angle of 65° to allow root growth along the agar surface and to allow unimpeded growth of the hypocotyl into the air. For plant growth, we used a plant growth cabinet (Percival Scientific, Perry, IA), with a photoperiod of 16 h light/8 h darkness, under a light intensity of 300 µmol m–2 s–1 and temperature of 22 to 24°C.
Mutant Isolation and Genetic Analysis
Gene Mapping and Molecular Confirmation
Cho and PCho Assays
Analysis of Root Architecture Traits
Expression Analysis in xipotl and S_036291 Seedlings by RT-PCR We followed the same protocol and conditions for control reactions and used specific primers for the Arabidopsis ß-tubulin gene TUB-RTF (5'-CTCAAGAGGTTCTCAGCAGTA-3') and TUB-RTR (5'-TCACCTTCTTCATCCGCAGTT-3').
Tissue Expression Analysis by RT-PCR We followed the same protocol and conditions for control reactions and used specific primers for the Arabidopsis ß-tubulin gene TUB-RTF (5'-CTCAAGAGGTTCTCAGCAGTA-3') and TUB-RTR (5'-TCACCTTCTTCATCCGCAGTT-3').
PA Inhibition by 1-Butanol
PA Assays Eight-day-old seedlings from mutant and wild-type plants that were grown on PA plates and MS medium plates with no PA were cleared and observed using the same procedure as previously described for Cho and PCho assays. Plants from each treatment were also stained with PI and Evans blue and observed under the same conditions described for Cho and PCho assays.
Whole Mount in Situ Hybridization
Determination of PCho and Cho Contents
Determination of Total PtdCho Content
Confocal Microscopy For single staining with PI, fresh roots were transferred to a solution of 10 µg/mL of this dye for 3 min. Imaging was monitored with a 568-nm excitation line and an emission window of 585 to 610 nm for PI.
Image Processing and Root Cell Size Determination
Sequence data from this article have been deposited with the EMBL/GenBank data libraries under accession numbers AF367299 (mRNA of At3g18000), AF428454 (mRNA of At1g48600), AY136372 (complete coding sequence of At1g73600), and NM_112553 (mRNA of PLD
The authors wish to thank Marcelina García-Aguilar, Willson Huanca-Mamani, and Anahí Pérez-Torres for their support in the whole mount in situ hybridization experiments and Jorge Molina-Torres for his help with the TLC experiments. We are especially grateful to Teun Munnik and Gert-Jan Deboer for their invaluable advice and comments on phospholipid determination experiments. We also thank June Simpson, John Délano-Frier, and Jean Phillipe Vielle-Calzada for critically reviewing this manuscript. This work was supported in part by the Consejo Nacional de Ciencia y Tecnología, México (Grant 31628-B), the European Commission (Grant ICA-4-CT2000-30017), and by the Howard Hughes Medical Institute (Grant Nbr55003677). A.C.R. was supported by the Consejo Nacional de Ciencia y Tecnología, México (fellowship 137977). We are grateful to the Genomic Analysis Laboratory at the Salk Institute for providing the sequence-indexed Arabidopsis T-DNA insertion mutants.
1 Current address: Centro de Estudios Avanzados en Zonas Aridas, Casilla 599, La Serena, Chile.  The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Luis Herrera-Estrella (lherrera{at}ira.cinvestav.mx). Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.103.018648. Received October 24, 2003; accepted May 10, 2004.
Allan, D. (2000). Lipid metabolic changes caused by short-chain ceramides and the connection with apoptosis. Biochem. J. 345, 603–610. Arisz, S.A., Valianpour, F., van Gennip, A.H., and Munnik, T. (2003). Substrate preference of stress-activated phospholipase D in Chlamydomonas and its contribution to PA formation. Plant J. 34, 595–604.[Medline] Bennett, M.J., Marchant, A., Green, H.G., May, S.T., Ward, S.P., Millner, P.A., Walker, A.R., Schulz, B., and Feldmann, K.A. (1996). Arabidopsis AUX1 gene: A permease-like regulator of root gravitropism. Science 273, 948–950.[Abstract]
Bolognese, C.P., and McGraw, P. (2000). The isolation and characterization in yeast of a gene for Arabidopsis S-adenosylmethionine:phosphoethanolamine N-methyltransferase. Plant Physiol. 124, 1800–1813.
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. Chaves, I., Regalado, A.P., Chen, M., Ricardo, C., and Showalter, A.M. (2002). Programmed cell death induced by (ß-D-galactosyl)3 Yariv reagent in Nicotiana tabacum BY-2 suspension-cultured cells. Physiol. Plant 116, 548–553.[CrossRef]
Cui, Z., Houweling, M., Chen, M.H., Record, M., Chap, H., Vance, D.E., and Terce, F. (1996). A genetic defect in phosphatidylcholine biosynthesis triggers apoptosis in Chinese hamster ovary cells. J. Biol. Chem. 271, 14668–14671.
Cui, Z., and Vance, D.E. (1996). Expression of phosphatidylethanolamine N-methyltransferase-2 is markedly enhanced in long-term choline-deficient rats. J. Biol. Chem. 271, 2839–2843.
Datko, A.H., and Mudd, S.H. (1988a). Enzymes of phosphatidylcholine synthesis in Lemna, soybean and carrot. Plant Physiol. 88, 1338–1348.
Datko, A.H., and Mudd, S.H. (1988b). Phosphatidylcholine synthesis. Plant Physiol. 88, 854–861. de Almeida, J., van Montagu, M., and Engler, G. (1998). Whole-mount in situ hybridization in plants. In Methods in Molecular Biology: Arabidopsis Protocols, J.M. Martínez-Sapater and J. Salinas, eds (Totowa, NJ: Humana Press), pp. 373–384. Den Hartog, M., Musgrave, A., and Munnik, T. (2001). Nod factor-induced phosphatidic acid and diacylglycerol pyrophosphate formation: A role for phospholipase C and D in root hair deformation. Plant J. 25, 55–66.[CrossRef][Web of Science][Medline]
Dhonukshe, P., Laxalt, A.M., Goedhart, J., Gadella, T.W.J., and Munnik, T. (2003). Phospholipase D activation correlates with microtubule reorganization in living plant cells. Plant Cell 15, 2666–2679. Exton, J.H. (1994). Phosphatidylcholine breakdown and signal transduction. Biochim. Biophys. Acta 1212, 26–42.[Medline]
Frank, W., Munnik, T., Kerkmann, K., Salamini, F., and Bartels, D. (2000). Water deficit triggers phospholipase D activity in the resurrection plant Craterostigma plantagineum. Plant Cell 12, 111–124.
Katagiri, T., Takahashi, S., and Shinozaki, K. (2001). Involvement of a novel Arabidopsis phospholipase D, AtPLD Kinney, A.J., and Moore, T.S., Jr. (1987). Phosphatidylcholine synthesis in castor bean endosperm: The localization and control of CTP:choline-phosphate cytidylyltransferase activity. Arch. Biochem. Biophys. 259, 15–21.[Medline] Kirik, V., Bouyer, D., Schöbinger, U., Bechtold, N., Herzog, M., Boneville, J.M., and Hülskamp, M. (2001). CPR5 is involved in cell proliferation and cell death control and encodes a novel transmembrane protein. Curr. Biol. 11, 1891–1895.[CrossRef][Web of Science][Medline] Laxalt, A.M., and Munnik, T. (2002). Phospholipid signalling in plant defence. Curr. Opin. Plant Biol. 5, 332–338.[CrossRef][Web of Science][Medline] Lee, S., Suh, S., Kim, S., Crain, R.C., Kwak, J.M., Nam, H.G., and Lee, Y. (1997). Systemic elevation of phosphatidic acid and lysophospholipid levels in wounded plants. Plant J. 12, 547–556.[CrossRef] Liu, Y.G., Mitsukawa, N., Oosumi, T., and Whittier, R. (1995). Efficient isolation and mapping of Arabidopsis thaliana T-DNA insert junctions by thermal asymmetric interlaced PCR. Plant J. 8, 457–463.[CrossRef][Web of Science][Medline] López-Bucio, J., Cruz-Ramírez, A., and Herrera-Estrella, L. (2003). The role of nutrient availability in regulating root architecture. Curr. Opin. Plant Biol. 6, 280–287.[CrossRef][Web of Science][Medline] López-Bucio, J., Hernández-Abreu, E., Sánchez-Calderón, L., Nieto-Jacobo, M.F., and Herrera-Estrella, L. (2002). Phosphate availability alters architecture and causes changes in hormone sensitivity in the Arabidopsis root system. Plant Physiol. 129, 144–156. Malamy, J.E., and Benfey, P.N. (1997). Organization and cell differentiation in lateral roots of Arabidopsis thaliana. Development 124, 33–44.[Abstract]
McGraw, P., and Henry, S.A. (1989). Mutations in the Saccharomyces cerevisiae opi3 gene: Effects on phospholipid methylation, growth and cross-pathway regulation of inositol synthesis. Genetics 122, 317–330.
McNeil, S.D., Nuccio, M.L., Rhodes, D., Shachar-Hill, Y., and Hanson, A.D. (2000). Radiotracer and computer modeling evidence that phospho-base methylation is the main route of choline synthesis in tobacco. Plant Physiol. 123, 371–380.
McNeil, S.D., Nuccio, M.L., Ziemak, M.J., and Hanson, A.D. (2001). Enhanced synthesis of choline and glycine betaine in transgenic tobacco plants that overexpress phosphoethanolamine N-methyltransferase. Proc. Natl. Acad. Sci. USA 98, 10001–10005. Meijer, H.J.G., and Munnik, T. (2003). Phospholipid-based signaling in plants. Annu. Rev. Plant Biol. 54, 265–306.[CrossRef][Medline]
Mergemann, H., and Sauter, M. (2000). Ethylene induces epidermal cell death at the site of adventitious root emergence in rice. Plant Physiol. 124, 609–614. Min Lee, M., and Schiefelbein, J. (1999). WEREWOLF, a MYB-related protein in Arabidopsis, is a position-dependent regulator of epidermal cell patterning. Cell 99, 473–483.[CrossRef][Web of Science][Medline] Monks, D.E., Goode, J.H., and Dewey, R.E. (1996). Characterization of soybean choline kinase cDNAs and their expression in yeast and Escherichia coli. Plant Physiol. 110, 1197–1205.[Abstract] Moreau, P., Bessoule, J.J., Mongrand, S., Testet, E., Vincent, P., and Cassagne, C. (1998). Lipid trafficking in plant cells. Prog. Lipid Res. 37, 371–391.[CrossRef][Web of Science][Medline]
Mou, Z., He, Y., Dai, Y., Liu, X., and Li, J. (2000). Deficiency in fatty acid synthase leads to premature cell death and dramatic alterations in plant morphology. Plant Cell 12, 405–417.
Mou, Z., Wang, X., Fu, Z., Dai, Y., Han, C., Ouyang, J., Bao, F., Hu, Y., and Li, J. (2002). Silencing of phosphoethanolamine N-methyltransferase results in temperature-sensitive male sterility and salt hypersensitivity in Arabidopsis. Plant Cell 14, 2031–2043. Munnik, T. (2001). Phosphatidic acid: An emerging plant lipid second messenger. Trends Plant Sci. 6, 227–233.[CrossRef][Web of Science][Medline] Munnik, T., Irvine, R.F., and Musgrave, A. (1994). Rapid turnover of phosphatidyl inositol 3-phosphate in the green alga Chlamydomonas eugametos: Signs of a phosphatidylinositide 3-kinase signaling pathway in lower plants. Biochem. J. 298, 269–273. Munnik, T., Irvine, R.F., and Musgrave, A. (1998). Phospholipid signalling in plants. Biochim. Biophys. Acta 1389, 222–272.[Medline] Nuccio, M.L., Russell, B.L., Nolte, K.D., Rathinasabapathi, B., Gage, D.A., and Hanson, A.D. (1998). The endogenous choline supply limits glycine betaine synthesis in transgenic tobacco expressing choline monooxygenase. Plant J. 16, 487–496.[CrossRef][Web of Science][Medline]
Nuccio, M.L., Ziemak, M.J., Henry, S.A., Weretilnyk, E.A., and Hanson, A.D. (2000). cDNA cloning of phosphoethanolamine N-methyltransferase from spinach by complementation in Schizosaccharomyces pombe and characterization of the recombinant enzyme. J. Biol. Chem. 275, 14095–14101.
Obeid, L.M., Linardic, C.M., Karolak, L.A., and Hannun, Y.A. (1993). Programmed cell death induced by ceramide. Science 259, 1769–1771.
Ohashi, Y., Oka, A., Rodrigues-Pousada, R., Possenti, M., Ruberti, I., Morelli, G., and Aoyama, T. (2003). Modulation of phospholipid signaling by GLABRA2 in root-hair pattern formation. Science 300, 1427–1430. Potocky, M., Elias, M., Profotová, B., Novotná, Z., Valentová, O., and Zarsky, V. (2003). Phosphatidic acid produced by phospholipase D is required for tobacco pollen tube growth. Planta 217, 122–130.[Web of Science][Medline]
Prud'homme, M.P., and Moore, T.S. (1992). Phosphatidylcholine synthesis in castor bean endosperm: The occurrence of an S-adenosyl-L-methionine:ethanolamine N-methyltransferase. Plant Physiol. 100, 1536–1540.
Qin, C., and Wang, X. (2002). The Arabidopsis phospholipase D family. Characterization of a calcium-independent and phosphatidylcholine-selective PLD Ramos, B., Salido, G.M., Campo, M.L., and Claro, E. (2000). Inhibition of phosphatidylcholine synthesis precedes apoptosis induced by C2-ceramide: Protection by exogenous phosphatidylcholine. Neuroreport 11, 3103–3108.[Medline]
Reire, J., Feldmann, K., and Marks, D. (1994). The GLABRA2 gene encodes a homeodomain protein required for normal trichome development in Arabidopsis. Genes Dev. 8, 1388–1399.
Schiefelbein, J. (2000). Constructing a plant cell. The genetic control of root hair development. Plant Physiol. 124, 1525–1531. Smith, D.D., Summers, P.S., and Weretilnyk, E.A. (2000). Phosphocholine synthesis in spinach: Characterization of phosphoethanolamine N-methyltransferase. Physiol. Plant 108, 286–294.[CrossRef] Vaux, D.L., and Korsmeyer, S.J. (1999). Cell death in development. Cell 96, 245–254.[CrossRef][Web of Science][Medline]
Wang, C., and Wang, X. (2001). A novel phospholipase D of Arabidopsis that is activated by oleic acid and associated with the plasma membrane. Plant Physiol. 127, 1102–1112.
Wang, X. (1999). The role of phospholipase D in signaling cascades. Plant Physiol. 120, 645–652. Wang, X. (2001). Plant phospholipases. Annu. Rev. Plant Physiol. Plant Mol. Biol. 52, 211–231.[CrossRef][Web of Science][Medline] Wang, X. (2002). Phospholipase D in hormonal and stress signaling. Curr. Opin. Plant. Biol. 5, 408–414.[CrossRef][Web of Science][Medline]
Yen, C.L., Mar, M.H., and Zeisel, S.H. (1999). Choline deficiency-induced apoptosis in PC12 cells is associated with diminished membrane phosphatidylcholine and sphingomyelin, accumulation of ceramide and diacylglycerol, and activation of a caspase. FASEB J. 13, 135–142.
Zhang, W., Wang, C., Qin, C., Wood, T., Olafsdottir, G., Welti, R., and Wang, X. (2003). The oleate-stimulated phospholipase D, PLD Zhou, X., and Arthur, G. (1992). Improved procedure for the determination of lipid phosphorous by malachite green. J. Lipid Res. 33, 1233–1236.[Abstract] This article has been cited by other articles:
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ABSTRACT
INTRODUCTION
1 as a sustrate-specific enzyme responsible for the breakdown of PtdCho into PA and Cho (Qin and Wang, 2002
-null protoplasts, is partially inhibited by exogenous PA, supporting the notion that the inhibition of PA biosynthesis in specific cell layers is directly involved in the xipotl cell death phenotype. 
