OsbZIP62/OsFD7, a functional ortholog of Flowering Locus D (FD), regulates floral transition and panicle development in rice

Abstract

We have characterized a rice bZIP protein coding gene OsbZIP62/OsFD7 that expresses preferentially in SAM and during early panicle developmental stages in comparison to other OsFDs characterised till date. Surprisingly, unlike OsFD1, OsFD7 interacts directly and more efficiently with OsFTLs; the interaction is strongest with OsFTL1 followed by Hd3a and RFT1, as confirmed by FLIM-FRET analysis. Also, OsFD7 is phosphorylated at its C-terminal end by OsCDPK41 and OsCDPK49 in vitro and this phosphorylated moiety is recognized by OsGF14 proteins. OsFD7 RNAi transgenics were late flowering; the transcript levels of some floral meristem identity genes (e.g. OsMADS14, OsMADS15 and OsMADS18) were also down-regulated. It was quite interesting to note that these RNAi lines exhibited dense panicle morphology with increase in the number of primary and secondary branches resulting in longer panicles and more seeds probably due to downregulation of Sepallata (SEP) family genes. In comparison to other FD-like proteins characterized thus far from rice, it appears that OsFD7 may have undergone diversification during evolution resulting in the acquisition of newer functions and thus playing dual role in floral transition and panicle development in rice. HighlightOsbZIP62/OsFD7 interacts with major flowering regulators participating in the processes of floral transition as well as panicle and floral organ development.