GA-mediated spatial control of cell division expounds the leaf size variation between cultivated and wild rice

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. SummaryHigh Gibberellic Acid level promotes cell division and cell production rate in rice leaves to increase the leaf length.