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ABSTRACT: How cells acquire competence to differentiate according to position is an essential question in developmental biology. Maize leaves provide a unique opportunity to study positional information. In the developing leaf primordium, a line is drawn across a field of seemingly identical cells. Above the line, the cells become blade, below the line the cells become sheath and at the line, the cells differentiate into the specialized tissues of ligule and auricle. We identified a new mutation, Liguleless narrow (Lgn), that affects this patterning and shows striking defects in lateral growth as well, thus linking proximal-distal patterning to medial-lateral growth. In characterizing the defect we discovered that both the auxin transport protein ZmPIN1a and the squamosa promoter-binding protein LIGULELESS1 are expressed precisely at this positionally cued line and are disrupted by Lgn. Positional cloning and a transposon-derived allele demonstrate that LGN is a kinase. These results suggest that LGN participates in setting up positional information through a signaling cascade. Interestingly, LGN has a paralog that is upregulated in the mutant, suggesting an important feedback mechanism involved in setting the positional boundary.
Development 01/2013; 140:405-412. · 6.60 Impact Factor
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ABSTRACT: Leaves are formed from a group of initial cells within the meristem. One of the earliest markers of leaf initiation is the down-regulation of KNOX genes in initial cells. Polar auxin activity, MYB and LOB domain transcription factors function to keep KNOX out of the initiating leaf. If KNOX genes are expressed in initial cells, leaves fail to form. As the leaf grows away from the meristem, its shape is determined by growth in three axes, proximal-distal, abaxial-adaxial and medial-lateral. HD-ZIPIII, KANADI and the small RNA pathway play a significant role in the latter two axes. KNOX proteins play a role in the proximal-distal axis. Although genetic networks are conserved between monocots and dicots, the outcome in leaf shape often differs.
Current opinion in plant biology 02/2011; 14(1):24-30. · 10.33 Impact Factor
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ABSTRACT: Although several genes have been identified in rice which are functionally equivalent to the flowering time genes in Arabidopsis, primarily genes involved in the photoperiod pathway, little data is available regarding the genes that function in the autonomous pathway in rice. In order to acquire further insight into the control of heading dates in rice, we isolated and conducted an expression analysis on OsFCA, which exhibited 38% sequence homology with Arabidopsis FCA. The N-terminal region of the OsFCA protein appears to be unusually rich in glycine-residues, unlike the N-terminal region found in FCA. However, the genetic structure of OsFCA is, in general, similar to that of FCA. RT-PCR and in silico analyses also showed that alternative splicing and polyadenylation at intron3 were conserved in the genetic expression of OsFCA. We were able to detect alpha, beta, and gamma transcripts, but not the delta transcript, of the OsFCA gene. The beta and gamma transcripts of the OsFCA gene were detected via Northern analysis in the leaves, roots, and flowers of the plant. Flowers in younger stages exhibited higher transcript levels. These data suggest that intron3 may constitute a primary control point in the OsFCA pre-mRNA processing of rice. The overexpression of OsFCA cDNA, driven by the 35S promoter, was shown to partially rescue the late flowering phenotype of the fca mutant, suggesting that the functions of the OsFCA and the FCA are partially overlapped, despite the lack of an apparent FLC homologue in the rice genome. The constitutive expression of OsFCA resulted in no downregulation of FLC, but did result in the weak upregulation of SOC1 in the transgenic Arabidopsis. OsFCA overexpression did not result in a reduction of the gamma transcript levels of FCA in the transgenic Arabidopsis either, thereby suggesting that OsFCA had no effects on the autoregulation of Arabidopsis FCA. All of these results imply conservation and divergence in the functions of FCA between rice and Arabidopsis.
Plant Molecular Biology 09/2005; 58(6):823-38. · 4.15 Impact Factor
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ABSTRACT: Flowering is regulated by an integrated network of several genetic pathways in Arabidopsis. The key genes integrating multiple flowering pathways are FT, SOC1 and LFY. To elucidate the interactions among these integrators, genetic analyses were performed. FT and SOC1 share the common upstream regulators CO, a key component in the long day pathway, and FLC, a flowering repressor integrating autonomous and vernalization pathways. However, the soc1 mutation further delayed the flowering time of long day pathway mutants including ft, demonstrating that SOC1 acts partially independently of FT. Although soc1 did not show an obvious defect in flower meristem determination on its own, it dramatically increased the number of coflorescences in a lfy mutant, which is indicative of a defect in floral initiation. Therefore, double mutant analysis shows that the three integrators have both overlapping and independent functions in the determination of flowering time and floral initiation. The expression analysis showed that FT regulates SOC1 expression, and SOC1 regulates LFY expression, but not vice versa, which is consistent with the fact that FT and LFY have the least overlapping functions among the three integrators. The triple mutation ft soc1 lfy did not block flowering completely under long days, indicating the presence of other integrators. Finally, vernalization accelerated flowering of flc ft soc1 and ft soc1 lfy triple mutants, which shows that the vernalization pathway also has targets other than FLC, FT, SOC1 and LFY. Our genetic analysis reveals the intricate nature of genetic networks for flowering.
Plant and Cell Physiology 03/2005; 46(2):292-9. · 4.70 Impact Factor
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Hyoun-Joung Kim,
Youbong Hyun,
Jin-Young Park,
Mi-Jin Park,
Mi-Kyung Park,
Myoung Duck Kim,
Hye-Joung Kim,
Mi Hyun Lee, Jihyun Moon,
Ilha Lee,
Jungmook Kim
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ABSTRACT: Cold induces expression of a number of genes that encode proteins that enhance tolerance to freezing temperatures in plants. A cis-acting element responsive to cold and drought, the C-repeat/dehydration-responsive element (C/DRE), was identified in the Arabidopsis thaliana stress-inducible genes RD29A and COR15a and found in other cold-inducible genes in various plants. C/DRE-binding factor/DRE-binding protein (CBF/DREB) is an essential component of the cold-acclimation response, but the signaling pathways and networks are mostly unknown. Here we used targeted genetic approach to isolate A. thaliana mutants with altered cold-responsive gene expression (acg) and identify ACG1 as a negative regulator of the CBF/DREB pathway. acg1 flowered late and had elevated expression of FLOWERING LOCUS C (FLC), a repressor of flowering encoding a MADS-box protein. We showed that acg1 is a null allele of the autonomous pathway gene FVE. FVE encodes a homolog of the mammalian retinoblastoma-associated protein, a component of a histone deacetylase (HDAC) complex involved in transcriptional repression. We also showed that plants sense intermittent cold stress through FVE and delay flowering with increasing expression of FLC. Dual roles of FVE in regulating the flowering time and the cold response may have an evolutionary advantage for plants by increasing their survival rates.
Nature Genetics 03/2004; 36(2):167-71. · 35.53 Impact Factor
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ABSTRACT: The floral transition in Arabidopsis is regulated by at least four flowering pathways: the long-day, autonomous, vernalization, and gibberellin (GA)-dependent pathways. Previously, we reported that the MADS-box transcription factor SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) integrates the long-day and vernalization/autonomous pathways. Here, we present evidences that SOC1 also integrates signaling from the GA-dependent pathway, a major flowering pathway under non-inductive short days. Under short days, the flowering time of GA-biosynthetic and -signaling mutants was well correlated with the level of SOC1 expression; overexpression of SOC1 rescued the non-flowering phenotype of ga1-3, and the soc1 null mutant showed reduced sensitivity to GA for flowering. In addition, we show that vernalization-induced repression of FLOWERING LOCUS C (FLC), an upstream negative regulator of SOC1, is not sufficient to activate SOC1; positive factors are also required. Under short days, the GA pathway provides a positive factor for SOC1 activation. In contrast to SOC1, the GA pathway does not regulate expression of other flowering integrators FLC and FT. Our results explain why the GA pathway has a strong effect on flowering under short days and how vernalization and GA interact at the molecular level.
The Plant Journal 10/2003; 35(5):613-23. · 6.16 Impact Factor
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ABSTRACT: The Arabidopsis CONSTANS (CO) gene is a key regulator of the long day (LD)-dependent flowering pathway and two CO homologous genes COL1 and COL2 are involved in the regulation of the circadian rhythm. In order to understand the role of CO and COL in short-day plants, a CO homologue, PnCOL1, was isolated and characterized from Japanese morning glory (Pharbitis nil). The deduced PnCOL1 protein of 386 amino acid residues contained two putative zinc finger motifs at the N-terminal region and a conserved CCT domain at the C-terminal region. The deduced amino acid sequence of PnCOL1 was 34% identical to that of PnCO, but 32%, 34%, and 34% identical to those of CO, COL1, and COL2, respectively. Expression of PnCOL1 was barely detected in the cotyledons of plants grown under continuous light (CL), but highly expressed in the cotyledons of plants grown under SD. Expression of PnCOL1 showed a pattern of circadian rhythm as well as daily oscillation. The overexpression of PnCOL1 by a 35S promoter did not overcome the late-flowering phenotype of Arabidopsis co mutants. The results provided in this study suggest that PnCOL1 may have a role in the circadian rhythm in Pharbitis nil.
Journal of Experimental Botany 09/2003; 54(389):1879-87. · 5.36 Impact Factor
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ABSTRACT: The MADS box gene, AGAMOUS-LIKE 20 (AGL20), integrates environmental and endogenous flowering signals in Arabidopsis thaliana. In order to determine if its role is conserved in other plants, we isolated AGL20 orthologs from Brassica campestris, Cardamine flexuosa and Draba nemorosa. The putative amino acid sequences of the orthologs were 94 to 97% identical. We analyzed the flowering phenotype and expression level of the AGL20 ortholog in C. flexuosa, a long day plant that does not respond to vernalization. CaAGL20 was more highly expressed in long days than short days and its expression did not change in response to vernalization, indicating that its expression is correlated with flowering time, as in Arabidopsis. When the Brassica AGL20 ortholog was constitutively expressed in sense and antisense orientations using the 35S cauliflower mosaic virus promoter, some of the sense transgenic plants flowered extremely early and some of the antisense plants exhibited delayed flowering. These results suggest that the role of AGL20 is conserved in Crucifers.
Molecules and Cells 09/2003; 16(1):136-41. · 2.18 Impact Factor
