A COBRA-like protein ACL83 acts downstream of transcription factor ROC5 to control abaxial leaf curling in rice

Leaf rolling is considered an important agronomic trait in rice (Oryza sativa). Moderate leaf rolling contributes to erect leaves and a compact plant architecture, thereby improving photosynthetic efficiency and grain yield. However, the molecular mechanisms regulating leaf rolling remain incompletely understood. In this study, we isolated an acl83 mutant in indica rice, which exhibits abaxially curled leaves due to increased area of bulliform cells. Map-based cloning and MutMap analysis revealed the candidate gene LOC_Os05g32110 (ACL83) encoding a COBRA-like protein. Complementation and CRISPR/Cas9 knockout assays confirmed that ACL83 is responsible for the mutant phenotype of acl83. ACL83 was constitutively expressed, and its encoded protein was localized to the plasma membrane. Furthermore, the transcription factor ROC5 directly bound to the promoter of ACL83 to activate ACL83 expression. Meanwhile, the acl83/roc5 double mutant exhibited an abaxially curled leaf phenotype similar to that of the acl83 single mutant, suggesting that ACL83 is a downstream target gene of ROC5. Collectively, our findings revealed a distinct ROC5-ACL83 genetic pathway in which the COBRA-like protein ACL83 functions downstream of ROC5 to control abaxial leaf rolling in rice by regulating cell expansion. This work provides insight into the role of COBRA-like proteins in the regulation of leaf morphogenesis.