The transcription factor MYB44 suppresses starch synthesis to negatively regulate grain weight and yield in wheat and rice.

Starch is the primary storage compound in wheat grains and is essential for both flour quality and grain weight. In this study, we identified TaMYB44, an R2R3-MYB transcription factor gene that controls starch content in wheat grains, through a genome-wide association study. The TaMYB44 homoeologs were predominantly expressed in developing grains, with peak levels observed 10 days after pollination. Functional analyses revealed that TaMYB44 acts as a negative regulator of starch synthesis in the endosperm, limiting grain size by repressing starch synthesis-related genes and modulating secondary metabolism. Knockout mutants of TaMYB44 exhibited significantly increased starch accumulation, larger grain size, and improved yield stability across diverse growing environments. Furthermore, we discovered that TaWDR1 interacts with TaMYB44, alleviating its repressive effects to restore starch synthesis and enhance grain weight. Notably, the functions of MYB44 appear to be partially conserved between wheat and rice, underscoring its potential as a target for genetic improvement. Our findings offer valuable insights into the transcriptional regulation of starch synthesis and provide genetic resources for enhancing grain yield in wheat and rice.