Epidermal Cell Dynamics Regulates Rice Lamina Joint Morphogenesis and Leaf Angle Formation through <i>OsZHD1</i> and <i>OsZHD2</i> Regulation

The lamina joint is a critical determinant of leaf angle and crop architecture. While epidermal cells play a fundamental role in organ morphogenesis, influencing the overall shape and function of plants, their impact on lamina joint morphology has been largely overlooked. A live-imaging system for the rice lamina joint epidermis is established in this study, enabling precise tracking of cellular dynamics during leaf angle formation. It is found that asymmetric elongation between the lateral and medial edges, determined by spatial differences in the longitudinal elongation and number of epidermal cells, is a key factor in leaf angle formation. Mutations in the homeobox genes OsZHD1 and OsZHD2 disrupt the growth patterns of lamina joint epidermal cells, resulting in a decreased leaf angle. Epidermis-specific restoration of OsZHD1 expression rescues the reduced leaf angle phenotype of oszhd1 oszhd2, confirming the pivotal role of epidermal development in lamina joint morphogenesis. Transcriptomic analysis indicates that OsZHD1 and OsZHD2 regulate auxin activity, which modulates leaf angle by restricting lamina joint epidermal growth. This study underscores the significance of epidermal cells in shaping the lamina joint and elucidates the critical role of OsZHD1 and OsZHD2 in regulating epidermal cell behavior and leaf angle formation.