OsvWA36 modulates rice grain length via intrinsically disordered region-mediated phase separation to control cell wall remodeling

Abstract Grain length is a critical agronomic trait that directly determines rice yield. In this study, we identified OsvWA36, a von Willebrand factor A (VWA) domain protein containing intrinsically disordered regions (IDRs). We showed that it is a novel positive regulator of grain length and that its function is achieved through liquid-liquid phase separation (LLPS) and subsequent modulation of cell wall remodeling.OsvWA36 was discovered through proteomic screening, and its abundance was positively correlated with grain length. It preferentially accumulated in developing panicles and formed liquid-like condensates via IDR-mediated LLPS, as indicated by in vitro/in vivo assays and fluorescence recovery after photobleaching analysis. CRISPR-Cas9-generated osvwa36 mutants developed shorter grains due to reductions in glume cell length and the aberrant accumulation of lignin. Transcriptomic and qRT-PCR analyses revealed that deficiency in OsvWA36 suppressed the expression of genes associated with cell wall dynamics, including those involved in cellulose synthesis (OsCESA4, OsCESA7, and OsCSLE1), pectin metabolism (OsPME68, OsPME1), and lignin modification (OsCAD2, OsMYB58, and OsExo70H3). Genetic complementation restored the wild-type phenotype, whereas overexpression of OsvWA36 further elongated grains. Deletion of the IDR domain abolished LLPS and resulted in short grains, phenocopying the osvwa36 mutants and underscoring the functional necessity of phase separation. Furthermore, haplotype analysis revealed that natural variation in OsvWA36 was correlated with grain length diversity in rice cultivars.In conclusion, our findings indicate that OsvWA36 regulates grain length by orchestrating cell wall remodeling through IDR-mediated LLPS and could be a useful target for molecular breeding strategies aimed at improving yield.