OsMADS22 interacts with OsMADS50 to regulate floral transition in rice

Appropriate flowering time is critical for reproductive transition and is closely related to crop yield. In Arabidopsis, SVP, MADS-box containing proteins, interact with FLC to form a repressor complex to repress the expression level of SOC1 and FT to control flowering time. OsMADS22, one of three SVP-clade MADS-box genes, has been shown that functions as a negative regulator on floral transition in rice. However, the molecular mechanism of OsMADS22 in flowering time and genetic interaction between SVP and SOC1 homologs was unknown. In this study, we found that OsMADS22 could form homodimers and interact with OsMADS50, a putative rice ortholog of SOC1, to antagonistically regulate key flowering-related genes, including OsMADS14, RFT1, Ehd1, Hd3a, and OsMADS1. Notably, elevated expression levels of OsMADS22 were detected in osmads50 mutants, whereas the transcript abundance of OsMADS50 remained unchanged under OsMADS22-overexpressing line compared with wild-type controls, suggesting that OsMADS50 is not genetically epistatic to OsMADS22, unlike their homologs in Arabidopsis. Moreover, we showed that the interaction between OsMADS22 and OsMADS50 is mainly dependent on their K-box domains. OsMADS50 localize to the nucleus while its Arabidopsis homolog SVP localized in cytosol. Notably, we newly revealed additional roles for OsMADS50 in rice grain development. Taken together, our results elucidate the regulatory pathways of OsMADS22 on flowering time and reveal species-specific functional divergence between SVP and SOC1 in Arabidopsis and their homologs in rice, providing new insights into flowering time regulation in rice.