The OsRhoGAP2-OsRAC5 complex regulates rice seed germination via modulating aleurone layer development and α-amylase...

Seed germination is a key agronomic trait that underpins seedling establishment in rice. Here, we show that the OsRhoGAP2-OsRAC5 protein complex positively regulates rice seed germination through modulating aleurone layer development and α-amylase activity. This study uncovers the role of Rho-GTPase signaling in controlling cereal seed germination and identifies candidate genes for molecular breeding of rice. The aleurone layer (AL) is a pivotal tissue controlling cereal seed germination, which governs hydrolytic enzyme synthesis and endosperm reserve remobilization in rice. Rho small GTPases and GTPase-activating proteins (RhoGAPs) play crucial roles in plant development; however, their specific functions in rice seed germination remain incompletely elucidated. Here, we demonstrated that OsRAC5, a Rho GTPase, acts as a key positive regulator of rice seed germination by controlling AL development. CRISPR-associated protein 9 (CRISPR/Cas9)-generated loss-of-function rac5 mutants displayed delayed germination, accompanied by a thinner AL and reduced α-amylase activity. Protein-protein interaction assays including Y2H, LCA, and BiFC confirmed that OsRAC5 physically interacts with OsRhoGAP2. Consistently, rhogap2 mutants phenocopied rac5 defects in AL formation, germination performance and α-amylase activity. Collectively, we uncovered that the OsRhoGAP2-OsRAC5 complex orchestrates rice seed germination via coordinating AL development and α-amylase-mediated reserve mobilization. This complex provides valuable gene resources and a mechanistic basis for molecular improvement of seedling establishment in rice breeding.