Recently, the rice scientific research team of Huazhong Agricultural University has analyzed the molecular complex model of rice adapting to long-day flower formation in research, providing a new way to regulate the regional adaptability of rice varieties and increase yield.
The molecular mechanism of plant flowering regulation is relatively conservative, and”florigen” (florigen) is generally formed in the phloem of leaves.”Florigen” is transported through vascular bundles to the apical meristem to form the Florigen activation complex (FAC), which initiates the plant’s transition from vegetative growth to reproductive growth. Therefore, the formation of florigen activating complex determines the time of plant flowering and the area where crop varieties are planted. Rice is an important food crop and a model plant for genome research. The heading date determines the seasonal and regional adaptability of the variety and is one of the important factors affecting its yield.
Although rice is easy to induce heading (flower conversion) under short-day conditions, after long-term artificial selection, a large number of rice varieties suitable for timely heading at high latitudes (long-day conditions) have been cultivated. Two important flowering genes Hd3a and RFT1 have been identified in the rice genome. They are the main genes that promote earing under short-day and long-day conditions, respectively. Under short-day conditions, the floridin Hd3a interacts with the 14-3-3 receptor protein to form the Hd3a/14-3-3 complex, and then combines with the OsFD1 protein in the stem apical meristem to form the floridin activation complex Promote the conversion of rice into flowers. However, the molecular mechanism of the formation of the florigen activation complex in rice under long-day conditions is still unclear.
Molecular model of rice florigen activation complex
Researchers through yeast two-hybrid, GST pull-down, BIFC and other experiments, found that RFT1 through 14-3-3 protein and phosphorylated flower formation promoter gene OsFD1 protein interaction to form a ternary florigen activation complex Therefore, it performs the function of initiating the conversion of rice into flowers under long-day conditions. Studies have found that the phosphorylation modification of Serine 192 (S192) residue in OsFD1 is essential for the formation of florigen activation complex. Further using protein interaction experiments to identify a protein kinase OsCIPK3 responsible for the phosphorylation of OsFD1. Biochemical analysis shows that OsCIPK3 protein has protein kinase activity, and it is proved that OsCIPK3 can phosphorylate and modify the 192nd serine position of OsFD1 protein. The phosphorylation modification of OsFD1 facilitates the entry of the florigen activation complex into the nucleus and promotes the conversion of rice from vegetative growth to reproductive growth.
Genetic analysis showed that the OsCIPK3 mutant showed late heading under long-day conditions, but the heading time under short-day conditions was consistent with that of the wild type. The OsCIPK3 mutation significantly increased the number of branches and spikelets of the panicle, and the yield per plant in the field experiment increased by more than 40%, indicating that the OsCIPK3 gene has important breeding value. Further analysis of biochemical experiments showed that OsCIPK3 is mainly responsible for the phosphorylation modification of OsFD1 protein under long-day conditions, and other protein kinases may participate in the phosphorylation modification of OsFD1 under short-day conditions, thereby forming a florigen activation complex.
Heading date is a critical trait that determine the regional adaptability and grain productivity in many crops. Although rice is a facultative short-day plant, its domestication led to the Ghd7-Ehd1-Hd3a/RFT1 pathway to adapt for long-day conditions (LDs). The formation of’florigen activation complex’ (FAC) containing florigen Hd3a has been elucidated. However, the molecular composition of FAC with RFT1 for long-day flowering are unclear. We show that RFT1 forms a ternary FAC with 14 -3-3 proteins and OsFD1 for flowering under LDs. The calcineurin B-like-interacting protein kinase, OsCIPK3, directly interacts with OsFD1 and phosphorylates OsFD1, which could facilitate FAC to localize in the nucleus. Mutation in OsCIPK3 results in a late heading date under LDs but normal heading date under short-day conditions (SDs). Our results suggest that OsCIPK3 phosphorylates OsFD1 for RFT1-containing FAC formation to initiate flowering in rice under LDs.
link to the paper:https://www.cell.com/molecular-plant/fulltext/S1674-2052(21)00126-X