Functional divergence of GhAP1.1 and GhFUL2 associated with flowering regulation in upland cotton (Gossypium hirsutum L.)
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Bimolecular fluorescence complementation
Leafy
AP-1 transcription factor
MYB
Bimolecular fluorescence complementation
Leafy
AP-1 transcription factor
MYB
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Higher plants continuously and iteratively produce new above-ground organs in the form of leaves, stems and flowers. These organs arise from shoot apical meristems whose homeostasis depends on coordination between self-renewal of stem cells and their differentiation into organ founder cells. This coordination is stringently controlled by the central transcription factor WUSCHEL (WUS), which is both necessary and sufficient for stem cell specification in Arabidopsis thaliana ULTRAPETALA1 (ULT1) was previously identified as a plant-specific, negative regulator of WUS expression. However, molecular mechanisms underlying this regulation remain unknown. ULT1 protein contains a SAND putative DNA-binding domain and a B-box, previously proposed as a protein interaction domain in eukaryotes. Here, we characterise a novel partner of ULT1, named ULT1 INTERACTING FACTOR 1 (UIF1), which contains a Myb domain and an EAR motif. UIF1 and ULT1 function in the same pathway for regulation of organ number in the flower. Moreover, UIF1 displays DNA-binding activity and specifically binds to WUS regulatory elements. We thus provide genetic and molecular evidence that UIF1 and ULT1 work together in floral meristem homeostasis, probably by direct repression of WUS expression.
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Leafy
Primordium
AP-1 transcription factor
Transcription
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Abstract Flowering (inflorescence formation) of the grass Lolium temulentum is strictly regulated, occurring rapidly on exposure to a single long day (LD). During floral induction, L. temulentum differs significantly from dicot species such as Arabidopsis in the expression, at the shoot apex, of twoAPETALA1 (AP1)-like genes, LtMADS1 andLtMADS2, and of L. temulentum LEAFY(LtLFY). As shown by in situ hybridization,LtMADS1 and LtMADS2 are expressed in the vegetative shoot apical meristem, but expression increases strongly within 30 h of LD floral induction. Later in floral development,LtMADS1 and LtMADS2 are expressed within spikelet and floret meristems and in the glume and lemma primordia. It is interesting that LtLFY is detected quite late (about 12 d after LD induction) within the spikelet meristems, glumes, and lemma primordia. These patterns contrast with Arabidopsis, whereLFY and AP1 are consecutively activated early during flower formation. LtMADS2, when expressed in transgenic Arabidopsis plants under the control of theAP1 promoter, could partially complement the organ number defect of the severe ap1-15 mutant allele, confirming a close relationship between LtMADS2 andAP1.
Leafy
Primordium
AP-1 transcription factor
Lemma (botany)
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Bimolecular fluorescence complementation
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Leafy
Silique
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Flowering plants produce floral meristems in response to intrinsic and extrinsic flowering inductive signals. In Arabidopsis, the floral meristem identity genes LEAFY (LFY) and APETALA1 (AP1) are activated to play a pivotal role in specifying floral meristems during floral transition. We show here that the emerging floral meristems require AP1 to partly specify their floral identities by directly repressing a group of flowering time genes, including SHORT VEGETATIVE PHASE (SVP), AGAMOUS-LIKE 24 (AGL24) and SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1). In wild-type plants, these flowering time genes are normally downregulated in emerging floral meristems. In the absence of AP1, these genes are ectopically expressed, transforming floral meristems into shoot meristems. By post-translational activation of an AP1-GR fusion protein and chromatin immunoprecipitation assays, we further demonstrate the repression of these flowering time genes by induced AP1 activity and in vivo AP1 binding to the cis-regulatory regions of these genes. These findings indicate that once AP1 is activated during the floral transition, it acts partly as a master repressor in floral meristems by directly suppressing the expression of flowering time genes, thus preventing the continuation of the shoot developmental program.
Leafy
AP-1 transcription factor
Agamous
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Leafy
Agamous
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MYB
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Leafy
Ectopic expression
AP-1 transcription factor
Lateral shoot
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