Rice OsIAA6 interacts with OsARF1 and regulates leaf inclination

Leaf inclination, a component of crop architecture, influences photosynthetic efficiency and planting density. Various factors, particularly the phytohormones auxin and brassinosteroids (BRs), function in regulating lamina joint bending, and understanding of the genetic control of leaf inclination will help to elucidate the relevant regulatory network. Screening a rice T-DNA insertion population revealed a mutant that was insensitive to auxin and displayed an enlarged leaf angle due to increased cell length on the adaxial side of the lamina joint. Genetic analysis revealed that the increased leaf inclination was caused by T-DNA insertion in the promoter region of OsIAA6 , resulting in elevated OsIAA6 expression. Further study showed that OsIAA6 interacts with OsARF1 to suppress auxin signaling and regulates leaf inclination. OsIAA6 mediates the BR effects on lamina joint development, and OsBZR1, the key transcription factor in BR signaling, binds directly to the promoter of OsIAA6 to stimulate its transcription. These results indicate the roles of the OsIAA6–OsARF1 module in regulating rice leaf inclination and suggest the synergistic effects of the phytohormones auxin and BR.