Abstract
Key flowering genes, FD and FD PARALOGUE (FDP) encoding bZIP transcription factors that interact with a FLOWERING LOCUS T (FT) in Arabidopsis were ectopically expressed in rice since we found AtFD and AtFDP also interact with HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T 1 (RFT1). Transgenic rice plants overexpressing AtFD and AtFDP caused reduction in plant height and spikelet size with decreased expression of genes involved in cell elongation without significant flowering time alteration in spite of increased expression of OsMADS14 and OsMADS15, rice homologues of APETALA1 (AP1) in the leaves. Simultaneous overexpression of AtFD and AtFDP enhanced phenotypes seen with overexpression of either single gene while transgenic rice plants expressing AtFD or AtFDP under the control of phloem-specific Hd3a promoter were indistinguishable from wild-type rice. Candidate genes responsible for the phenotypes were identified by comparison of microarray hybridization and their expression pattern was also examined in WT and transgenic rice plants. It has so far not been reported that AtFD and AtFDP affect cell elongation in plants, and our findings provide novel insight into the possible roles of AtFD and AtFDP in the mesophyll cells of plants, and potential genetic tools for manipulation of crop architecture.
Highlights
Formation of a hexameric florigen activation complex (FAC) composed of a rice florigen HEADING DATE 3a (Hd3a), GF14 proteins (14-3-3 s) and phosphorylated transcription factor OsFD1 has been reported to activate OsMADS15, a homologue of Arabidopsis APETALA1 (AP1) resulting in flowering[1]
To test whether Arabidopsis FD and FD PARALOGUE (FDP) are able to interact with rice Hd3a or RICE FLOWERING LOCUS T 1 (RFT1), rice FLOWERING LOCUS T (FT) homologues, we utilized yeast two-hybrid systems and got positive results for Hd3a, RFT1, AtFD and AtFDP
AtFD and AtFDP proteins were co-localized with Hd3a and RFT1 in the nucleus of rice protoplasts derived from mesophyll cells (Supplementary Fig. S1)
Summary
Formation of a hexameric florigen activation complex (FAC) composed of a rice florigen Hd3a, GF14 proteins (14-3-3 s) and phosphorylated transcription factor OsFD1 has been reported to activate OsMADS15, a homologue of Arabidopsis APETALA1 (AP1) resulting in flowering[1]. FT homologues are known to play various roles in plant developmental processes it remains unknown whether formation of FAC-like complexes is necessarily required for their function. GF14c knock-out mutant rice is seedling-lethal and transgenic rice with GF14c overexpression show delayed flowering[19] Even though it is still unknown whether all interactions between FT homologues and bZIP proteins are dependent on 14-3-3s, published data demonstrated that a FAC-like complex containing OsFD2 possesses the same components required for the formation of FAC, but is implicated in rice leaf development
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