OsvWA36 transcriptionally regulates cell wall remodeling to control grain length in rice.

Grain length is a crucial determinant of rice yield and quality. Although von Willebrand factor type A (VWA) domain proteins have recently emerged as regulators of plant architecture in cereals, their roles in controlling rice grain length remain largely unexplored. Here, we report the functional characterization of OsvWA36, a VWA-domain protein selected from a TMT-based quantitative proteomic screen of indica rice varieties differing in grain length. Loss-of-function OsvWA36 mutants exhibited significantly reduced grain length and thousand-grain weight, while complementation and overexpression assays confirmed its positive regulatory role in these traits. Cytological analysis revealed that the shortened grain phenotype was due to suppressed longitudinal elongation of hull epidermal cells, which was accompanied by aberrantly enhanced lignin deposition. Transcriptomic profiling and Gene Ontology (GO) enrichment analysis demonstrated that OsvWA36 is essential for the expression of a comprehensive suite of cell wall biosynthesis and modification genes, including those involved in cellulose, pectin, and lignin metabolism. Furthermore, OsvWA36 localizes to punctate structures on the endoplasmic reticulum (ER). Our study establishes OsvWA36 as a novel VWA-domain protein that positively regulates grain length by orchestrating cell wall remodeling programs, thereby bridging VWA protein function with the transcriptional regulation of cell wall dynamics in rice. This work not only identifies a promising genetic target for molecular breeding but also provides a new molecular framework for understanding grain size regulation in cereal crops.