The BELL-KNOX module qSH1-OSH71 regulates rice seed shattering via direct activation of OsXTH12 xyloglucanase

Rice (Oryza sativa L.) seed shattering is an important agronomic trait closely associated with yield. This study identified the interaction between Oryza sativa HOMEOBOX 71 (OSH71) and the essential seed shattering gene quantitative trait locus of seed shattering on chromosome 1 (qSH1) in rice. Mutants of OSH71 exhibited defects in abscission zone (AZ) development, leading to reduced seed shattering. Importantly, both qSH1 and OSH71 directly bound to the promoter of xyloglucan endotransglucosylase/hydrolase (OsXTH12) and activated its expression, with their interaction further enhancing promoter activity. OsXTH12 mutants showed decreased seed shattering, which was consistent with the findings for OSH71 mutants. Glucuronidase staining assays revealed OSH71 and OsXTH12 genes were highly induced in the AZ of young panicles, indicating the role of the qSH1-OSH71-OsXTH12 module in AZ development. OsXTH12-overexpressing lines showed a decrease in hemicellulose content in the AZ, leading to increased seed shattering in rice. Furthermore, ethylene levels increased in the OsXTH12-overexpressing lines. This study investigated the molecular mechanisms by which the qSH1-OSH71-OsXTH12 pathway regulates rice seed shattering, laying the foundation for deciphering the molecular modules involved in rice seed shattering regulation.