The OsMYB4 transcription factor enables coordinated improvement of grain yield and quality in rice.

The endosperm is the predominant storage organ for starch and storage proteins in cereal grains, which also determines both grain yield and quality. Although key enzymes involved in the biosynthesis of starch and storage proteins have been identified, the underlying regulatory mechanisms remain largely obscure. In this study, we identified OsMYB4, a MYB transcription factor, specifically expressed in rice (Oryza sativa L.) endosperm. Loss-of-function of OsMYB4 led to increased grain chalkiness, accompanied by reduced amylose and protein contents as well as decreased grain yield. OsMYB4 directly binds to the promoters of multiple genes involved in starch and storage protein synthesis to activate their transcription. It also forms protein complexes with multiple transcription factors to synergistically regulate grain yield and quality. In addition, OsMYB4 was directly activated by RISBZ1, a key regulator of storage reserve accumulation. Moreover, overexpression of OsMYB4 resulted in larger grains and enhanced yield. Notably, natural variation analysis revealed that the beneficial haplotype OsMYB4-Hap1 is positively associated with increased grain weight and superior quality. In conclusion, our results demonstrate the regulatory role of OsMYB4 for grain development, which provides valuable genetic resources for simultaneously improving grain yield and quality in rice.