OsDUF3615 regulates grain size and quality traits by modulating cell proliferation and starch metabolism in rice.

Domains of Unknown Function (DUFs) are widely distributed across diverse genomes and are increasingly recognized as important regulators of plant growth, development, and stress responses. DUF3615 is a highly conserved plant-specific protein motif; however, its biological function remains largely unknown. Previously, the gene OsGAPC3, a key regulator of grain quality, was isolated and functionally characterized in rice. Transcriptome analysis during the dissection of the OsGAPC3-mediated regulatory pathway revealed that OsDUF3615 is significantly upregulated in Osgapc3 mutants, suggesting its potential involvement in rice development and grain traits. In this study, we show that OsDUF3615 is constitutively expressed in rice and encodes a nucleus-localized protein. Functional analysis demonstrated that overexpression of OsDUF3615 significantly promotes cell proliferation and expansion in the lemma along the grain width axis, leading to increased grain width and thousand-grain weight. Moreover, OsDUF3615 modulates grain filling dynamics and alters the accumulation of major storage compounds, including starch and free fatty acids, thereby affecting both nutritional composition and eating quality traits, such as taste value. Collectively, our findings identify OsDUF3615 as a key regulator of rice grain development and quality formation, providing valuable genetic resources for the molecular breeding of high-quality rice varieties.