Rice has more complex and unique flowering pathway compared with that of Arabidopsis. Rice is a facultative short-day (SD) plant, flowers early in SD and late in long-day (LD) conditions. Conserved Heading date 1 (Hd1) and unique Early heading date 1 (Ehd1) are two major floral signal integrators that receive multiple signals from other genes to control the expression of the florigens (Tsuji et al. 2011). Heading date 3a (Hd3a) and RICE FLOWERING LOCUS T (RFT1) are the florigens produced in the leaf under inductive day length conditions and transported to the shoot apex where it triggers flowering transition (Cajlachjan, 1937; Corbesier et al., 2007; Tamaki et al., 2007). Unlike only one florigen gene FLOWERING LOCUS T (FT) in Arabidopsis, rice evolves two florigen genes, Hd3a and RFT1, and at least two flowering pathways are developed to control the expression of florigens. First one is the Heading date 1 (Hd1) pathway which is conserved between rice and Arabidopsis, and the Early heading date 1 (Ehd1) pathway which is unique to rice (Doi et al., 2004). In SD conditions, Ehd1 is controlled by OsGIGANTEA (OsGI), Early heading date 2 (Ehd2), and OsMAD51.
