Regulation of Flowering Time in Rice

Rice flowers after a lengthy vegetative growth. During the vegetative growth period flowering is inhibited by several independent pathways. Whereas Grain number, plant height, and heading date 7 (Ghd7), Heading date 1 (Hd1), Heading date 5 (Hd5), Heading date 6 (Hd6), and Heading date 16 (Hd16) preferentially function to delay flowering under long day conditions, Oryza sativa Phytochrome B (OsPhyB), Oryza sativa CONSTANS-like 4 (OsCOL4), SUPERNUMERARY BRACT (SNB) and Oryza sativa INDETERMINATE SPIKELET 1 (OsIDS1) independently inhibit flowering regardless of day length. After sufficient vegetative growth, flowering signals are produced in the leaves due to reduced expression of the inhibitors. In addition, Hd1 becomes a flowering promoter when the day length becomes shorter. Long-day specific activators OsMADS50 and OsDof12, and a constitutive activators Oryza sativa INDETERMINATE 1 (OsId1), Early heading date 4 (Ehd4), and miR172, are accumulated in the leaves when plants are grown sufficiently. Several circadian clock genes are also involved in floral transition, including Oryza sativa GIGANTEA (OsGI), Heading date 2 (Hd2), and Heading date 17 (Hd17). Floral transition is also controlled by photoreceptors and chromatin remodeling factors. Most of the upstream signals are transferred to Early heading date 1 (Ehd1) that is a positive regulator of Heading data 3a (Hd3a) and Rice FT 1 (RFT1), which are transferred to the shoot apical meristem to induce the reproductive transition.