Summary Cellular and genetic understanding of the rice leaf size regulation is limited, despite rice being the staple food of more than half of the global population. We investigated the mechanism controlling the rice leaf length using cultivated and wild rice accessions that remarkably differed for leaf size. Comparative transcriptomics, gibberellic acid (GA) quantification and leaf kinematics of the contrasting accessions suggested the involvement of GA, cell cycle and growth‐regulating factors (GRFs) in the rice leaf size regulation. Zone‐specific expression analysis and VIGS established the functions of specific GRFs in the process. The leaf length of the selected accessions was strongly correlated with GA levels. Higher GA content in wild rice accessions with longer leaves and GA‐induced increase in the leaf length via an increase in cell division confirmed a GA‐mediated regulation of division zone in rice. Downstream to GA, OsGRF7 and OsGRF8 function for controlling cell division to determine the rice leaf length. Spatial control of cell division to determine the division zone size mediated by GA and downstream OsGRF7 and OsGRF8 explains the leaf length differences between the cultivated and wild rice. This mechanism to control the rice leaf length might have contributed to optimizing leaf size during domestication.

Leaf size is a major determinant of crop performance by influencing leaf physiological processes, such as light capture, transpiration, and gas exchange. Therefore, understanding the genetic basis of leaf size regulation is imperative for crop improvement. Natural variation in leaf size for a crop plant is a valuable genetic resource for a detailed understanding of leaf size regulation. We investigated the mechanism controlling the rice leaf length using cultivated and wild rice accessions that showed remarkable differences for the leaf features. Comparative transcriptomic profiling of the contrasting accessions suggested the involvement of Gibberellic Acid (GA), Growth Regulating Factor (GRF) transcription factors, and cell cycle in the rice leaf size regulation. Leaf kinematics studies showed that the increased domain of cell division activity along with a faster cell production rate drove the longer leaves in the wild rice Oryza australiensis compared to the cultivated varieties. Higher GA levels in the leaves of Oryza australiensis, and GA-induced increase in the rice leaf length via an increase in cell division zone emphasized the key role of GA in rice leaf length regulation. Zone-specific expression and silencing of the GA biosynthesis and signaling genes confirmed that OsGRF7 and OsGRF8 function downstream to GA for controlling cell cycle to determine the rice leaf length. The GA-GRF-cell cycle module for rice leaf length regulation might have contributed to optimizing leaf features during the domestication and could also be a way for plants to achieve leaf plasticity in response to the environment.