OsWRKY11 Regulates Rice Leaf Angle Via Transcriptional Activation of OsGSR1.

Leaf angle is a key agronomic trait that determines plant architecture and grain yield in rice. Although brassinosteroids (BRs) are known to play a central role in regulating leaf angle, the upstream transcriptional regulatory network remains elusive. Here, we characterized the lla (large leaf angle) mutant which carried a T-DNA insertion in the promoter of OsWRKY11 (a WRKY transcription factor) and exhibits significantly enlarged leaf angles at both seedling and mature stages. We demonstrated that the large leaf angle phenotype of lla was caused by the T-DNA insertion in the promoter of OsWRKY11, leading to its pronounced upregulation. Overexpression of OsWRKY11 recapitulated the lla phenotype, whereas knockdown of OsWRKY11 in the lla background restored leaf angle to wild-type levels, establishing OsWRKY11 as a positive regulator of this trait. Interestingly, the lla mutants are hypersensitive to exogenous BR treatment and accumulate higher levels of the bioactive BR castasterone. Further analyses showed that OsWRKY11 directly binds to W-box elements in the promoter of OsGSR1(a GAST family protein), a known positive regulator of BR biosynthesis, and activates its transcription. Genetic analysis revealed that OsWRKY11 acts upstream of OsGSR1 in the same genetic pathway to regulate leaf angle. Together, our findings uncover an OsWRKY11-OsGSR1 module that fine-tunes leaf angle by modulating BR homeostasis.