The OsMAPK6-OsWRKY72 module positively regulates rice leaf angle through brassinosteroid signals

Leaf angle is a major agronomic trait that determines plant architecture, which directly affects rice planting density, photosynthetic efficiency, and yield. The plant phytohormones brassinosteroids (BRs) and the MAPK signaling cascade are known to play crucial roles in regulating the leaf angle, but the underlying molecular mechanisms are not fully understood. Here, we report a rice WRKY family transcription factor gene, OsWRKY72, which positively regulates leaf angle by affecting lamina joint development and BR signaling. Phenotypic analysis showed that oswrky72 mutants had smaller leaf angles and exhibited insensitive to exogenous brassinosteroid, while the OsWRKY72 overexpression lines led to enlarged leaf angles and were hypersensitive to exogenous BR. Histological sections indicated that the change in leaf inclination was due to asymmetric cell proliferation and growth at the lamina joint. Further investigation showed that OsWRKY72 directly bound to the promoter regions of BR receptor kinase (OsBRI1), a key gene in the BR signaling pathway, and activated its expression to positively regulates rice BR signaling. In addition, we discovered that OsWRKY72 can interact with OsMAPK6 and be phosphorylated, and this phosphorylation event enhanced OsWRKY72 activity in promoting OsBRI1 expression. The genetic evidence confirmed that OsMAPK6, OsWRKY72 and OsBRI1 functions in a common pathway to regulate leaf angles. Collectively, our findings elucidate the critical role of the transcription factor OsWRKY72 in regulating rice leaf angle. These results provided valuable insights into the molecular regulatory networks governing plant architecture in rice.