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First published online September 21, 2007; 10.1105/tpc.107.054528 The Plant Cell 19:2736-2748 (2007) © 2007 American Society of Plant Biologists OPEN ACCESS ARTICLE
The GIGANTEA-Regulated MicroRNA172 Mediates Photoperiodic Flowering Independent of CONSTANS in Arabidopsis[W],[OA]
a Molecular Signaling Laboratory, Department of Chemistry, Seoul National University, Seoul 151-742, Korea 1 Address correspondence to cmpark{at}snu.ac.kr.
Regulated RNA metabolism appears to be a critical component of molecular mechanisms directing flowering initiation in plants. A group of RNA binding proteins exerts their roles through the autonomous flowering pathway. Posttranscriptional mechanisms regulated by microRNAs (miRNAs) also play a key role in flowering-time control. Here, we demonstrate that the GIGANTEA (GI)-regulated miR172 defines a unique genetic pathway that regulates photoperiodic flowering by inducing FLOWERING LOCUS T (FT) independent of CONSTANS (CO). A late-flowering mutant in which a miR172 target gene, TARGET OF EAT1, is constitutively activated by the nearby insertion of the cauliflower mosaic virus 35S enhancer normally responded to vernalization and gibberellic acid treatments. By contrast, its response to daylength changes was severely disrupted. In the mutant, FT was significantly repressed, but other flowering genes were unaffected. Notably, miR172 abundance is regulated by photoperiod via GI-mediated miRNA processing. Accordingly, miR172-overproducing plants exhibit early flowering under both long days and short days, even in the absence of functional CO, indicating that miR172 promotes photoperiodic flowering through a CO-independent genetic pathway. Therefore, it appears that GI-mediated photoperiodic flowering is governed by the coordinated interaction of two distinct genetic pathways: one mediated via CO and the other mediated via miR172 and its targets.
Seasonal control of flowering is essential for reproductive success in plants and therefore regulated by coordinated interactions between various endogenous signals and environmental cues (Mouradov et al., 2002  ). Light is one of the most important environmental factors that substantially affect seasonal flowering. Environmental light is actually a complex factor consisting of diverse components, such as intensity, quality (wavelength), photoperiod, and directionality, among which effects of photoperiod and light quality are most prominent in flowering-time control (Cerdan and Chory, 2003; Hayama and Coupland, 2003).
Plants sense seasonal progression by monitoring the daily variation of photoperiod lengths through circadian rhythms that are generated by the clock system. The intimate relationship between circadian rhythms and photoperiodic flowering has been studied extensively (Samach and Coupland, 2000
CO promotes flowering in inductive light conditions by activating FT transcription. The role of CO is regulated at the transcriptional level by GI-mediated circadian rhythms as well as at the posttranscriptional level by the photoreceptors (Valverde et al., 2004
Regulated RNA metabolism is an important molecular scheme functioning in flowering-time control in plants. A group of genes encoding RNA binding proteins, including FPA, FCA, and FLK, regulates flowering initiation through the autonomous flowering pathway (Macknight et al., 1997
Of particular interest are microRNAs (miRNAs). Three miRNAs have been functionally characterized in flowering-time control: miR156 (Schwab et al., 2005
It has been observed that miR172 is regulated by daylength and that the daylength effect on miR172 is disrupted in the co and ft mutants (Schmid et al., 2003
In this work, we show that miR172 mediates photoperiodic flowering by regulating FT. The functional role of miR172 depends on GI but does not require functional CO, demonstrating that miR172 belongs to a unique photoperiod flowering pathway. Our data indicate that GI-mediated photoperiodic flowering is coordinately regulated by at least two distinct molecular schemes: one mediated by CO (Suárez-López et al., 2001
toe1-2D Is Late Flowering Due to TOE1 Overexpression We isolated a late-flowering mutant, toe1-2D, by screening an Arabidopsis activation-tagged mutant pool generated by randomly inserting the cauliflower mosaic virus (CaMV) 35S enhancer into the genome of ecotype Columbia-0 (Col-0) (Weigel et al., 2000 ). Except for the late-flowering phenotype, other growth and developmental aspects, such as growth rate and organ morphologies, were essentially normal in the mutant (Figure 1A
). The toe1-2D mutant initiated flowering at a rosette leaf number (RLN) of 22.6 ± 1.2 under LDs, whereas control plants flowered at a RLN of 11.6 ± 1.3 under the same growth conditions.
A three-step thermal asymmetric interlaced–PCR analysis revealed that TOE1 encoding an AP2 domain–containing transcription factor was activated by the nearby insertion of the 35S enhancer in the toe1-2D genome (Figure 1B). Genomic DNA gel blot analysis confirmed that there was a single T-DNA insertion event occurring in the mutant (see Supplemental Figure 1A online). The toe1-2D mutant is allelic to toe1-1D, a late-flowering mutant that was isolated previously by a similar approach (Aukerman and Sakai, 2003 ). By contrast, a T-DNA insertional knockout mutant, toe1, showed slightly early flowering (Figure 1A), as has been reported previously (Aukerman and Sakai, 2003), demonstrating that TOE1 overexpression underlies the late-flowering phenotype of toe1-2D (see Supplemental Figure 1B online).
TOE1 possesses two AP2 domains in similar positions as those identified in the homeotic protein AP2, but sequence similarities are entirely restricted to the AP2 domains (see Supplemental Figure 2 online) (Okamuro et al., 1997 TOE1 transcript level was high in very young seedlings but gradually decreased throughout the life cycle (Figure 1C). A similar pattern was also observed with TOE2 and SNZ. Notably, SMZ transcript level decreased more rapidly and was barely detectable in 3-week-old or older plants. By contrast, TOE3 exhibited a reversed expression pattern. Its expression was relatively low in young seedlings but increased rapidly as plants grew until flowering. The diverse expression patterns suggest that TOE3 may be functionally distinct from other AP2-like genes. To further examine the physiological roles of TOE1 and related genes targeted by miR172, transgenic plants overexpressing individual genes and T-DNA insertional mutants were obtained and their flowering phenotypes were measured. Whereas overexpression of TOE2, SNZ, or SMZ caused late flowering as in TOE1 (Figure 1D), TOE3 overexpression did not exhibit late flowering. The toe2, toe3, smz, and snz mutants were phenotypically indistinguishable from control plants and apparently normal in flowering phenotypes, unlike the toe1 mutant, suggesting a functional redundancy among the miR172 target genes. Consistent with this notion, the toe1 toe2 double mutant flowered earlier than the toe1 mutant (see Figure 6C below). These observations indicate that the miR172 target genes are differentially regulated and may play distinct as well as overlapping roles in flowering promotion and other developmental processes.
Levels of miR172 and TOE1 Transcript Are Mutually Complementary It has been shown that miR172 abundance increases as plants grow, and it regulates its target mRNAs primarily through translational repression (Aukerman and Sakai, 2003 ; Lauter et al., 2005). However, it was later shown that TOE1 mRNA is also cleaved by miR172, although the steady state mRNA level is unchanged due to feedback regulation (Schwab et al., 2005).
Transcript levels of four target genes, TOE1, TOE2, SMZ, and SNZ, were steadily reduced as plants grew. By contrast, miR172 abundance increased rapidly until flowering (Figure 2A
), as has been observed (Aukerman and Sakai, 2003
To obtain further insights into how miR172 regulates its targets, miR172 abundance and TOE1 transcript level were compared in plant tissues. We observed that levels of miR172 and TOE1 transcript exhibited a mutual complementarity in plant tissues, which is consistent with the proposed threshold model for miR172 function (Aukerman and Sakai, 2003 ). The relative levels of miR172 and TOE1 transcript were inversely related to each other in most plant tissues. For example, miR172 abundance was relatively high but TOE1 mRNA level was low in flowers, floral buds, and stem tissues (Figure 2B). In addition, miR172 was very low in root tissue in which TOE1 mRNA level was very high. These complementarities are likely to be caused by miR172-directed TOE1 mRNA cleavage occurring at least in these plant tissues. However, the mutual complementarity was not observed in leaf tissue. This may be due to different expression domains of miR172 and its targets or to feedback regulatory mechanisms in this tissue (Schwab et al., 2005). Notably, other miR172 target genes showed distinct spatial expression patterns. Transcript levels of TOE2, TOE3, and SMZ as well as AP2 were relatively high in flowers and floral buds but low in leaves and stems (see Supplemental Figure 3 online). Tissue-specific expression patterns of SNZ were most similar to those of TOE1, with comparatively high expression in leaves and stems, although the level was very low in roots. Together, these observations suggest that temporal and spatial regulation of the MIR172 genes and their targets would be important for their functions in flowering promotion and floral architecture.
Our data supported that at least TOE1 mRNA might be cleaved by miR172 (Figures 1C, 2A, and 2B). To more directly examine whether TOE1 mRNA is cleaved by miR172, we employed the Nicotiana benthamiana transient expression system (Llave et al., 2002
FT and Its Downstream Genes Are Downregulated in toe1-2D
The next question concerned the hierarchic relationship between miR172 and FT. It has been suggested that miR172 functions downstream of FT (Schmid et al., 2003 ). However, such FT dependence of miR172 abundance was not observed in another study (Aukerman and Sakai, 2003). To resolve this uncertainty, levels of pre-miR172 and mature miR172 were examined in the knockout ft-10 mutant (Yoo et al., 2005). We used floral tissues, since miR172 levels are highest in the adult reproductive stage (Figure 2A). The levels of pre-miR172 and miR172 were identical in the floral buds and fully open flowers of control and ft-10 plants (Figure 3B). It was anticipated that analysis using floral tissues would be confounded by the potential effects of different developmental stages. Therefore, we examined the levels of miR172 in young seedlings. Again, the miR172 levels were identical in control plants, 35S::FT transgenic plants, and ft mutants (see Supplemental Figure 5 online). Together with FT repression in toe1-2D and induction in toe1 (Figure 3A), these results indicate that FT functions downstream of miR172 and TOE1. Consistent with this view, ft-10 mutants overproducing miR172 still showed late flowering (Figure 3C), comparable with the parental mutant. Furthermore, the expression domains of FT and TOE1 were mutually complementary (Figure 3D; see Supplemental Figure 6 online). While GUS activity was primarily distributed in the distal leaf area in FT promoter–GUS transgenic plants, it was detected mainly in the proximal leaf area in TOE1 promoter–GUS transgenic plants, further supporting the functional relationship between FT and TOE1.
miR172 Abundance Is Altered in gi-2 and Photoreceptor Mutants
To obtain insights into how miR172 and TOE1 regulate photoperiodic flowering, miR172 abundance was examined in the co-2, gi-2, and various photoreceptor mutants. Interestingly, miR172 abundance was substantially reduced in gi-2 but unaffected in co-2 (Figure 4B). By contrast, it was greatly upregulated in toc1-1, a SD-specific early-flowering mutant (Somers et al., 1998 ). The level of miR172 was also altered in the photoreceptor mutants. Whereas it was reduced markedly in the cryptochrome mutants and slightly in phyA-211, it increased detectably in phyB-9. Furthermore, a dramatic increase was observed in hy1, a mutant that lacks functional phytochromes (Muramoto et al., 1999). These results are well consistent with the antagonistic roles of phyB and the cryptochromes in regulating photoperiodic flowering (Lin, 2000; El-Din El-Assal et al., 2003; Mockler et al., 2003). Consistent with the altered miR172 abundances in the photoreceptor mutants, it increased significantly after blue light illumination but decreased after red light illumination (Figure 4C). These observations support the notion that miR172 is regulated by GI but independent of CO through the photoperiod flowering pathway. However, TOE1 transcript level was unaltered in gi-2 (Figure 4D) as well as in co-2 and photoreceptor mutants (see Supplemental Figure 8 online), which is consistent with the fact that the miR172 regulation of target mRNAs occurs primarily at the level of translation. We additionally found that miR172 abundance was unaltered in ft-3 (Figure 4B). By contrast, FT transcription increased drastically in 172OX transgenic plants overexpressing MIR172a-1 (Figure 4E). Furthermore, miR172 abundance was much higher in plants grown under LDs but lower in plants grown under SDs (Figure 4F). Therefore, it is evident that miR172 functions upstream of FT in response to daylength changes.
miR172 Abundance Is Regulated by GI through miRNA Metabolism
To further examine the functional relationship between GI and miR172, the MIR172a-2 gene was overexpressed under the control of the CaMV 35S promoter in the gi-2 mutant. The resultant 35S::172 gi plants flowered at a RLN of 5.4 ± 0.9 (Figures 5C and 5D), demonstrating that miR172 functions downstream of GI, which is also consistent with the reduced miR172 abundance in the gi-2 mutant (Figure 5B). In addition, the miR172-overproducing fha-1 mutant (35S::172 cry2) also exhibited early flowering, initiating flowering at a RLN of 3.7 ± 0.9 (Figures 5C and 5D). Floral architecture of the transgenic plants was disrupted (Figure 5E), indicative of miR172 overproduction in the transgenic plants. miR172 abundance was reduced significantly in the gi-2 mutant (Figure 5B) and regulated by daylength (Figure 4F). A critical question, therefore, was how GI regulates miR172 abundance. To obtain insights into the molecular mechanisms by which GI regulates miR172 abundance, control and gi-2 plants grown for 3 weeks under SDs were transferred to LDs and further grown for 3 to 7 d, and levels of miR172 and MIR172 transcripts were examined. miR172 abundance increased upon transfer to LDs in both control and gi-2 plants, but with a considerably reduced rate in the latter (Figure 5F). Interestingly, MIR172 transcript levels were higher in the gi-2 mutant than in control plants when grown under SDs and were reduced slightly in both plants upon exposure to LDs. Therefore, it is likely that GI regulates miR172 maturation (processing) rather than MIR172 transcription. In accordance with this view, genes encoding miRNA processing enzymes, such as DCL1 and SE, were obviously reduced in the gi-2 mutant (Figure 5G).
miR172 Regulates the Amplitude of FT Expression but Not Its Daily Rhythm Our data indicate that miR172 abundance is regulated by daylength. It was relatively very low under SDs (Figures 4F and 5A), suggesting that the TOE1 activity would be higher under SDs. Therefore, it was assumed that the early-flowering phenotypes of toe1 would be more evident under SDs than under LDs. To examine this hypothesis, control and toe1 mutant plants were grown under LDs and SDs and their flowering times was compared. A toe1 toe2 double mutant was also included in the assays. While toe1 flowering was accelerated by 20.6% under LDs, it was accelerated by 44.2% under SDs compared with control plants (Figures 6C and 6D). The flowering acceleration was more evident in the toe1 toe2 double mutant. It was accelerated by 33.3% under LDs and by 56.5% under SDs. These results further support the regulation of miR172 by daylength and the role of TOE1 in flowering-time control. Consistent with the early-flowering phenotype of toe1 and toe1 toe2, transcript levels of FT, LFY, and AP1 were proportionally higher in the mutants (Figure 6E).
The miR172-Mediated Flowering Pathway Is Independent of CO
It is also envisioned that the flowering initiation of the 35S::172 co plants at a RLN of 7.2 ± 0.8 may reflect a maximal capacity of the miR172 pathway in promoting flowering in the absence of functional CO. Full functioning of FT may require both the CO- and miR172-mediated signals in photoperiodic flowering. This reasoning also explains why the 172OX flowering was delayed under SDs, when the CO-mediated FT induction became negligible, in the previous report (Aukerman and Sakai, 2003 ). Consistent with the early-flowering phenotype of the 35S::172 co plants both under LDs and SDs (Figure 7A), the transcript levels of FT were upregulated in the 35S::172 co plants regardless of daylength changes (Figure 7B), further confirming that miR172 promotes flowering by inducing FT in a CO-independent manner. Together, our data demonstrate that miR172 mediates clock-independent GI signals in regulating photoperiodic flowering via FT (Figure 7C). In this view, GI plays a dual role in photoperiodic flowering: circadian rhythmic regulation of CO expression and regulation of miR172 metabolism, both of which are required for FT function.
miR172 Abundance Is Influenced by Autonomous Pathway Mutations
To examine this possibility, miR172 abundance was examined in a series of mutants that belong to other flowering pathways. Although we found no discernible changes in miR172 abundance in the mutants functioning in the vernalization and GA pathways, it was significantly reduced in a few autonomous pathway mutants. While it was at least threefold lower in fca and flk and twofold lower in fy, a visible increase was observed in fve (Figure 8
). Other autonomous pathway mutations did not influence miR172 abundance to a detectable level, suggesting that there might be more than one signaling cascade in the autonomous pathway, as has been proposed previously (Simpson et al., 2003
miR172 in Photoperiodic Flowering miR172 is unique among the characterized miRNAs mediating flowering initiation in that it regulates both floral architecture and flowering time by controlling a group of AP2 domain–containing transcription factors. It regulates a floral organ identity gene, AP2, and a group of related genes, such as TOE1, TOE2, SMZ, and SNZ, through mRNA cleavage and translational repression (Schwab et al., 2005 ). Whereas plants overexpressing TOE1 are late-flowering with normal floral morphologies, mutations in AP2 exhibit altered floral structures without affecting flowering time (Okamuro et al., 1997). In addition, although TOE3 is a target of miR172, transgenic plants overexpressing TOE3 are not late-flowering. Furthermore, its expression profile is different from those of other targets (Figure 1C). It seems that miR172 exerts its role through multiple signaling pathways.
miR172 regulation of flowering time has also been demonstrated in N. benthamiana (Mlotshwa et al., 2006 There are five MIR172 genes in Arabidopsis. Whereas the expression of MIR172a-1, MIR172a-2, and MIR172b-1 is elevated as plants reach the reproductive growth stage, that of MIR172b-2 and MIR172c is very low and does not respond to growth stages, supporting the notion that the growth stage–dependent increase of miR172 abundance is regulated primarily at the transcriptional level. Furthermore, its target genes also show differential expression patterns spatially and temporally. It will be interesting to investigate transgenic plants or mutants with altered expression of individual genes or of multiple genes in terms of detailed aspects of flowering time and floral architecture, as well as other developmental aspects, such as seed germination.
miR172 was once suggested to function via the photoperiodic flowering pathway. It has been shown that the target genes are suppressed upon flowering and that this downregulation is dependent on CO and FT (Schmid et al., 2003
In this work, we analyzed the flowering phenotypes of diverse mutants and transgenic plants with altered miR172 abundance or with altered target gene expression. We observed that an activation-tagging mutant overexpressing the miR172 target TOE1 was late-flowering only under LDs but responded normally to vernalization and GA treatments, indicating that TOE1 belongs to the photoperiodic flowering pathway. miR172 abundance was regulated by daylength changes via GI. However, it was independent of CO. Based on our observations, we concluded that miR172 and its targets constitute a unique genetic pathway that regulates flowering time by mediating FT expression in response to daylength changes. In a previous report (Schmid et al., 2003
Our data suggest that GI regulates miR172 processing rather than transcription of the MIR172 genes. This view is also supported by the downregulation of DCL1 and SE in the gi-2 mutant. These results suggest that processing of additional miRNAs would also be regulated by GI. This notion would also explain the pleiotropic phenotypes associated with the gi mutants (Fowler et al., 1999
Physiological Role of miR172 in Flowering Initiation
Photoperiodic flowering requires diverse aspects of light signals, including photosensory signals that regulate CO protein stability and those resetting the circadian clock (Imaizumi and Kay, 2006
It has been observed that miR172 expression is temporally regulated (Aukerman and Sakai, 2003
Plant Materials and Growth Conditions The hy4, fha-1, hy1, ft-3, and co-2 mutants and the miR172-overproducing line (172OX) overexpressing MIR172a-1 under the control of the CaMV 35S promoter were in the Landsberg erecta ecotype. All other Arabidopsis thaliana lines used were in the Col-0 ecotype. The 172OX seeds were kindly provided by X. Chen (Rutgers University). Plants were grown in a controlled culture room set at 23°C with a RH of 60%. The photoperiods were 16 h of light and 8 h of dark for the LD conditions and 8 h of light and 16 h of dark for the SD conditions, with white light illumination (120 µmol·m–2·s–1) provided by FLR40D/A fluorescent tubes (Osram). For light wavelength treatments, plants were grown in darkness or under red, far-red, or blue light (12, 8, and 15 µmol·m–2·s–1, respectively) in a VS-940L-DUAL incubator (Vision) equipped with red, far-red, or blue light–emitting diodes.
A knockout mutant, toe1 (SALK 069677), which has a single T-DNA insertion into the sixth exon of TOE1, was isolated from a pool of T-DNA insertion lines (ABRC, Ohio State University). The absence of TOE1 expression in toe1 was confirmed by RT-PCR. The knockout mutant is identical to the toe1 mutant characterized by Aukerman and Sakai (2003)
Generation of miR172-Overproducing Plants and Arabidopsis Transformation
For transient expression of MIR172 genes and their targets in Nicotiana benthamiana leaf cells, the gene constructs were subcloned into the pB2GW7 Gateway vector (Invitrogen). Agrobacterial cells containing the vector constructs were injected directly into the leaves. miRNA was extracted from the leaves at 4 d after injection as described and analyzed on a 1.2% formaldehyde–agarose gel (Kim et al., 2005
Isolation of the toe1-2D Mutant
The single T-DNA insertion event in toe1-2D was verified by genomic DNA gel blot hybridization using the 35S enhancer sequence as a probe, followed by analysis of segregation ratios. The sequences flanking the T-DNA insertion site in toe1-2D were determined by three-step thermal asymmetric interlaced–PCR (Liu et al., 1995
Flowering-Time Measurements
Vernalization and GA Treatments
RNA Gel Blot Hybridization and DNA Gel Blot Hybridization of RT-PCR Products Prior to RT-PCR, total RNA samples were extensively pretreated with RNase-free DNaseI to eliminate any contaminating genomic DNA. To determine the linear amplification range for the RT-PCR of each gene, a certain amount (0.5 to 2 µg) of each total RNA sample was used for RT-PCR runs with different numbers of cycles (15 to 35 cycles). The RT-PCR products were subjected to DNA gel blot hybridization, and densitometric scores were plotted against the numbers of PCR cycles. RT-PCR runs were performed for 20 to 35 cycles, depending on the linear range of PCR amplification for each gene. Each PCR cycle included incubations at 94°C for 1 min, 55°C for 1 min, and 72°C for 5 min. One additional cycle at 72°C for 10 min was run after the last cycle to allow trimming of incomplete polymerizations. Whenever possible, positive and negative control genes were included in the reactions to ensure the feasibility of the assay conditions. For RT-PCR–based DNA gel blot hybridization, <10 ng of PCR products was analyzed on a 1% agarose gel and transferred to a Hybond-N+ nylon membrane (Amersham-Pharmacia). The membrane was hybridized with gene-specific probes labeled with [32P]dCTP using the Megaprime DNA labeling system (Amersham-Pharmacia). The primers used for the RT-PCR are listed in Supplemental Table 1 online. Quantitation of transcript levels was determined by densitometry of images using the Labwork image acquisition and analysis program (Media Cybernetics).
miRNA Extraction and RNA Gel Blot Hybridization
miRNA RNA gel blot hybridizations were performed using the ULTRA-Hyb Oligo solution according to the procedure supplied by the manufacturer (Ambion). The oligonucleotide probes were 5' end–labeled using [32P] For the detection and measurement of primary MIR172 transcripts, DNA gel blot hybridization of RT-PCR products was performed using the primer pairs described in Supplemental Table 1 online.
Supplemental Data
We thank X. Chen for providing the 172OX line and S.K. Kang for transformation of gi-2 and co-2 with the MIR172a-2 gene construct. This work was supported by the BK21, Biogreen21 (Grant 20050301034456), and National Research Laboratory (Grant 2005-01039) programs and by grants from the Plant Signaling Network Research Center and the Korea Research Foundation (Grant 2005-070-C00129).
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: Chung-Mo Park (cmpark{at}snu.ac.kr).
[W] Online version contains Web-only data.
[OA] Open Access articles can be viewed online without a subscription. www.plantcell.org/cgi/doi/10.1105/tpc.107.054528 Received July 25, 2007; Revision received August 24, 2007. accepted August 27, 2007.
Achard, P., Herr, A., Baulcombe, D.C., and Harberd, N.P. (2004). Modulation of floral development by a gibberellin-regulated microRNA. Development 131: 3357–3365. Aukerman, M.J., and Sakai, H. (2003). Regulation of flowering time and floral organ identity by a microRNA and its APETALA2-like target genes. Plant Cell 15: 2730–2741. Bezerra, I.C., Michaels, S.D., Schomburg, F.M., and Amasino, R.M. (2004). Lesions in the mRNA cap-binding gene ABA HYPERSENSITIVE 1 suppress FRIGIDA-mediated delayed flowering in Arabidopsis. Plant J. 40: 112–119.[CrossRef][Web of Science][Medline] Cerdan, P.D., and Chory, J. (2003). Regulation of flowering time by light quality. Nature 423: 881–885.[CrossRef][Medline] Chen, X. (2003). A microRNA as a translational repressor of APETALA2 in Arabidopsis flower development. Science 303: 2022–2025.[CrossRef][Web of Science][Medline] Chuck, G., Cigan, A.M., Saeteurn, K., and Hake, S. (2007). The heterochronic maize mutant Corngrass1 results from overexpression of a tandem microRNA. Nat. Genet. 39: 544–549.[CrossRef][Web of Science][Medline] Clough, S.J., and Bent, A.F. (1998). Floral dip: A simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. Plant J. 16: 735–743.[CrossRef][Web of Science][Medline] Davis, S.J. (2002). Photoperiodism: The coincidental perception of the season. Curr. Biol. 12: R841–R843.[CrossRef][Web of Science][Medline] Doi, K., Izawa, T., Fuse, T., Yamanouchi, U., Kubo, T., Shimatani, Z., Yano, M., and Yoshimura, A. (2004). Ehd1, a B-type response regulator in rice, confers short-day promotion of flowering and controls FT-like gene expression independently of Hd1. Genes Dev. 18: 926–936. Doyle, M.R., Bizzell, C.M., Keller, M.R., Michaels, S.D., Song, J., Noh, Y.S., and Amasino, R.M. (2005). HUA2 is required for the expression of floral repressors in Arabidopsis thaliana. Plant J. 41: 376–385.[CrossRef][Web of Science][Medline] El-Din El-Assal, S., Alonso-Blanco, C., Peeters, A.J., Wagemaker, C., Weller, J.L., and Koornneef, M. (2003). The role of Cryptochrome 2 in flowering in Arabidopsis. Plant Physiol. 133: 1504–1516. Fowler, S., Lee, K., Onouchi, H., Samach, A., Richardson, K., Morris, B., Coupland, G., and Putterill, J. (1999). GIGANTEA: A circadian clock-controlled gene that regulates photoperiodic flowering in Arabidopsis and encodes a protein with several possible membrane-spanning domains. EMBO J. 18: 4679–4688.[CrossRef][Web of Science][Medline] Hayama, R., and Coupland, G. (2003). Shedding light on the circadian clock and the photoperiodic control of flowering. Curr. Opin. Plant Biol. 6: 13–19.[CrossRef][Web of Science][Medline] Hayama, R., and Coupland, G. (2004). The molecular basis of diversity in the photoperiodic flowering responses of Arabidopsis and rice. Plant Physiol. 135: 677–684. He, Y., Doyle, M.R., and Amasino, R.M. (2004). PAF1-complex-mediated histone methylation of FLOWERING LOCUS C chromatin is required for the vernalization-responsive, winter-annual habit in Arabidopsis. Genes Dev. 18: 2774–2784. Hugouvieux, V., Kwak, J.M., and Schroeder, J.I. (2001). An mRNA cap binding protein, ABH1, modulates early abscisic acid signal transduction in Arabidopsis. Cell 106: 477–487.[CrossRef][Web of Science][Medline] Imaizumi, T., and Kay, S.A. (2006). Photoperiodic control of flowering: Not only by coincidence. Trends Plant Sci. 11: 550–558.[CrossRef][Web of Science][Medline] Kim, J., Jung, J.-H., Reyes, J.L., Kim, Y.-S., Kim, S.-Y., Chung, K.-S., Kim, J.-A., Lee, M., Lee, Y., Kim, V.N., Chua, N.-H., and Park, C.-M. (2005). MicroRNA-directed cleavage of ATHB15 mRNA regulates vascular development in Arabidopsis inflorescence stem. Plant J. 42: 84–94.[CrossRef][Web of Science][Medline] Koornneef, M., Hanhart, C.J., and van der Veen, J.H. (1991). A genetic and physiological analysis of late flowering mutants in Arabidopsis thaliana. Mol. Gen. Genet. 229: 57–66.[Web of Science][Medline] Lauter, N., Kampani, A., Carlson, S., Goebel, M., and Moose, S.P. (2005). microRNA172 down-regulates glossy15 to promote vegetative phase change in maize. Proc. Natl. Acad. Sci. USA 102: 9412–9417. Lim, M.H., Kim, J., Kim, Y.S., Chung, K.S., Seo, Y.H., Lee, I., Kim, J., Hong, C.B., Kim, H.J., and Park, C.M. (2004). A new Arabidopsis gene, FLK, encodes an RNA binding protein with K homology motifs and regulates flowering time via FLOWERING LOCUS C. Plant Cell 16: 731–740. Lin, C. (2000). Photoreceptors and regulation of flowering time. Plant Physiol. 123: 39–50. Liu, Y.G., Mitsukawa, N., Oosumi, T., and Whittier, R.F. (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] Llave, C., Xie, Z., Kasschau, K.D., and Carrington, J.C. (2002). Cleavage of Scarecrow-like mRNA targets directed by a class of Arabidopsis miRNA. Science 297: 2053–2056. Macknight, R., Bancroft, I., Page, T., Lister, C., Schmidt, R., Love, K., Westphal, L., Murphy, G., Sherson, S., Cobbett, C., and Dean, C. (1997). FCA, a gene controlling flowering time in Arabidopsis, encodes a protein containing RNA-binding domains. Cell 89: 737–745.[CrossRef][Web of Science][Medline] Michaels, S.D., and Amasino, R.M. (1999). Loss of FLOWERING LOCUS C activity eliminates the late-flowering phenotype of FRIGIDA and autonomous pathway mutations but not responsiveness to vernalization. Plant Cell 13: 935–941.[CrossRef] Mizoguchi, T., Wright, L., Fujiwara, S., Cremer, F., Lee, K., Onouchi, H., Mouradov, A., Fowler, S., Kamada, H., Putterill, J., and Coupland, G. (2005). Distinct roles of GIGANTEA in promoting flowering and regulating circadian rhythms in Arabidopsis. Plant Cell 17: 2255–2270. Mlotshwa, S., Yang, Z., Kim, Y., and Chen, X. (2006). Floral patterning defects induced by Arabidopsis APETALA2 and microRNA172 expression in Nicotiana benthamiana. Plant Mol. Biol. 61: 781–793.[CrossRef][Web of Science][Medline] Mockler, T., Yang, H., Yu, X., Parikh, D., Cheng, Y.C., Dolan, S., and Lin, C. (2003). Regulation of photoperiodic flowering by Arabidopsis photoreceptors. Proc. Natl. Acad. Sci. USA 100: 2140–2145. Mouradov, A., Cremer, F., and Coupland, G. (2002). Control of flowering time: Interacting pathways as a basis for diversity. Plant Cell 14 (suppl.): S111–S130. Muramoto, T., Kohchi, T., Yokota, A., Hwang, I., and Goodman, H.M. (1999). The Arabidopsis photomorphogenic mutant hy1 is deficient in phytochrome chromophore biosynthesis as a result of a mutation in a plastid heme oxygenase. Plant Cell 11: 335–348. Nelson, D.C., Lasswell, J., Rogg, L.E., Cohen, M.A., and Bartel, B. (2000). FKF1, a clock-controlled gene that regulates the transition to flowering in Arabidopsis. Cell 101: 331–340.[CrossRef][Web of Science][Medline] Noh, Y.S., and Amasino, R.M. (2003). PIE1, an ISWI family gene, is required for FLC activation and floral repression in Arabidopsis. Plant Cell 15: 1671–1682. Okamuro, J.K., Caster, B., Villarroel, R., Van Montagu, M., and Jofuku, K.D. (1997). The AP2 domain of APETALA2 defines a large new family of DNA binding proteins in Arabidopsis. Proc. Natl. Acad. Sci. USA 94: 7076–7081. Oliverio, K.A., Crepy, M., Martin-Tryon, E.L., Milich, R., Harmer, S.L., Putterill, J., Yanovsky, M.J., and Casal, J.J. (2007). GIGANTEA regulates phytochrome A-mediated photomorphogenesis independently of its role in the circadian clock. Plant Physiol. 144: 495–502. Park, D.H., Somers, D.E., Kim, Y.S., Choy, Y.H., Lim, H.K., Soh, M.S., Kim, H.J., Kay, S.A., and Nam, H.G. (1999). Control of circadian rhythms and photoperiodic flowering by the Arabidopsis GIGANTEA gene. Science 285: 1579–1582. Pfeffer, S., Lagos-Quintana, M., and Tuschl, T. (2003). Cloning of small RNA molecules. In Current Protocols in Molecular Biology, F.M. Ausubel, R. Brent, R.E. Kingston, D.D. Moore, J.G. Seidmann, J.A. Smith, and K. Struhl, eds (New York: John Wiley & Sons), p. 26. Putterill, J. (2001). Flowering in time: Genes controlling photoperiodic flowering in Arabidopsis. Philos. Trans. R. Soc. Lond. B Biol. Sci. 356: 1761–1767. Putterill, J., Laurie, R., and Macknight, R. (2004). It's time to flower: The genetic control of flowering time. Bioessays 26: 363–373.[CrossRef][Web of Science][Medline] Quesada, V., Dean, C., and Simpson, G.G. (2005). Regulated RNA processing in the control of Arabidopsis flowering. Int. J. Dev. Biol. 49: 773–780.[CrossRef][Web of Science][Medline] Razem, F.A., El-Kereamy, A., Abrams, S.R., and Hill, R.D. (2006). The RNA-binding protein FCA is an abscisic acid receptor. Nature 439: 290–294.[CrossRef][Medline] Samach, A., and Coupland, G. (2000). Time measurement and the control of flowering in plants. Bioessays 22: 38–47.[CrossRef][Web of Science][Medline] Schauer, S.E., Jacobsen, S.E., Meinke, D.W., and Ray, A. (2002). DICER-LIKE1: Blind men and elephants in Arabidopsis development. Trends Plant Sci. 7: 487–491.[CrossRef][Web of Science][Medline] Schmid, M., Uhlenhaut, N.H., Godard, F., Demar, M., Bressan, R., Weigel, D., and Lohmann, J.U. (2003). Dissection of floral induction pathways using global expression analysis. Development 130: 6001–6012. Schomburg, F.M., Patton, D.A., Meinke, D.W., and Amasino, R.M. (2001). FPA, a gene involved in floral induction in Arabidopsis, encodes a protein containing RNA-recognition motifs. Plant Cell 13: 1427–1436. Schwab, R., Palatnik, J.F., Riester, M., Schommer, C., Schmid, M., and Weigel, D. (2005). Specific effects of microRNAs on the plant transcriptome. Dev. Cell 8: 517–527.[CrossRef][Web of Science][Medline] Simpson, G.G., Dijkwel, P.P., Quesada, V., Henderson, I., and Dean, C. (2003). FY is an RNA 3' end-processing factor that interacts with FCA to control the Arabidopsis floral transition. Cell 113: 777–787.[CrossRef][Web of Science][Medline] Somers, D.E., Schultz, T.F., Milnamow, M., and Kay, S.A. (2000). ZEITLUPE encodes a novel clock-associated PAS protein from Arabidopsis. Cell 101: 319–329.[CrossRef][Web of Science][Medline] Somers, D.E., Webb, A.A., Pearson, M., and Kay, S.A. (1998). The short-period mutant, toc1-1, alters circadian clock regulation of multiple outputs throughout development in Arabidopsis thaliana. Development 125: 485–494.[Abstract] Suárez-López, P., Wheatley, K., Robson, F., Onouchi, H., Valverde, F., and Coupland, G. (2001). CONSTANS mediates between the circadian clock and the control of flowering in Arabidopsis. Nature 410: 1116–1120.[CrossRef][Medline] Valverde, F., Mouradov, A., Soppe, W., Ravenscroft, D., Samach, A., and Coupland, G. (2004). Photoreceptor regulation of CONSTANS protein in photoperiodic flowering. Science 303: 1003–1006. Weigel, D., et al. (2000). Activation tagging in Arabidopsis. Plant Physiol. 122: 1003–1013. Yang, L., Liu, Z., Lu, F., Dong, A., and Huang, H. (2006). SERRATE is a novel nuclear regulator in primary microRNA processing in Arabidopsis. Plant J. 47: 841–850.[CrossRef][Web of Science][Medline] Yanovsky, M.J., and Kay, S.A. (2002). Molecular basis of seasonal time measurement in Arabidopsis. Nature 419: 308–312.[CrossRef][Medline] Yanovsky, M.J., and Kay, S.A. (2003). Living by the calendar: How plants know when to flower. Nat. Rev. Mol. Cell Biol. 4: 265–275.[CrossRef][Web of Science][Medline] Yoo, S.K., Chung, K.S., Kim, J., Lee, J.H., Hong, S.M., Yoo, S.J., Yoo, S.Y., Lee, J.S., and Ahn, J.H. (2005). CONSTANS activates SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 through FLOWERING LOCUS T to promote flowering in Arabidopsis. Plant Physiol. 139: 770–778. This article has been cited by other articles:
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TOP
ABSTRACT
INTRODUCTION
TOE1) of the TOE1 gene used in the mRNA cleavage assays. It was used instead of a full-size one, since the miR172 cleavage site is located near the 3' end. ORF, open reading frame; UTR, untranslated region.
400 bases were used instead of full-size gene sequences to more clearly discriminate the cleavage products (
ATP and T4 polynucleotide kinase. An oligonucleotide complementary to 5S rRNA was also processed in the same way and used as a quality control for RNA preparations. 
