OsPM19L Coordinates Phytohormone Signaling to Regulate Axillary Bud Outgrowth and Regeneration in Ratoon Rice

Ratoon rice cultivation is an efficient production system that achieves a second harvest from the stubble of the main crop, but its yield potential is largely constrained by variation in axillary bud regeneration capacity. Here, we identify <i>OsPM19L</i>, a plasma membrane-localized AWPM-19 domain protein, as a key regulator of rice ratooning ability. Transcriptome analysis revealed higher <i>OsPM19L</i> expression in strong-regeneration cultivars, followed by a sharp decline after harvest. Promoter assays and hormonal treatments demonstrated that <i>OsPM19L</i> is strongly induced by ABA and functions as a positive regulator in ABA signaling. Under field conditions, <i>ospm19l</i> mutants exhibited increased tiller number but reduced ratooning index, whereas <i>OsPM19L-OE</i> plants showed the opposite pattern, indicating stage-specific regulation of tillering and regeneration. Hormone profiling and gene expression analyses showed that <i>OsPM19L</i> is associated with altered levels of multiple phytohormones in regenerating axillary buds, showing higher CK and GA levels and lower IAA and ABA levels in <i>OsPM19L-OE</i> compared with the wild type. Consequently, <i>OsPM19L</i> appears to facilitate dormancy release and enhance early axillary bud growth during the ratoon season. These findings indicate <i>OsPM19L</i> may act as a central regulator linking ABA signaling with hormonal cross-talk, providing new insights into the molecular control of regeneration and potential targets for improving ratoon rice productivity.