Rice florigen gene Hd3a has conserved functions in callus development

Abstract

The transition of meristems is an important developmental process for crop plants. Florigen is considered to be produced in leaves, then moves into the shoot apical meristem (SAM), triggers the transition from the vegetative to the reproductive phase. However, little is known whether Florigen functions in callus development or not. By fused reporter gene β-glucuronidase (GUS) to 1.7 kb promoter of Heading date 3a (Hd3a), GUS signals were detected in the scutellum cells, as well as in green point of the putative transgenic calli. Quantitative RT-PCR results demonstrated that the expression level of Hd3a was increased gradually over time along with the transition from scutellum-deprived callus to shoot. As reported that ectopic expression of FT-like genes caused earlier flowering, we also found that 80% constitutive expression of Hd3a transgenic callus showed formation floral-like organ structures. However, Hd3a RNA interference (RNAi) transgenic calli did not show any obvious phenotype, although AP1 or AP1-like genes—OsMADS14, OsMADS15, and OsMADS18- expression level is decreased during callus development. Both in Hd3a and RFT1 overexpression transgenic calli, Hd3a also modulated AP1 or AP1-like genes, as well AEPALLATA (SEP)-like gene, OsMADS34 during green point formation. Meanwhile, transgenic calli of RFT1and OsMADS50, but not OsEhd1, shared similar results as Hd3a. All of these findings suggested that florigen genes Hd3a and RFT1 have partial conserved functions in the transition of meristems during callus development.