The wall-associated kinase GWN1 controls grain weight and grain number in rice.

Grain size is a crucial agronomic trait that determines grain weight and final yield. Although several genes have been reported to regulate grain size in rice (Oryza sativa), the function of Wall-Associated Kinase family genes affecting grain size is still largely unknown. In this study, we identified GRAIN WEIGHT AND NUMBER 1 (GWN1) using map-based cloning. GWN1 encodes the OsWAK74 protein kinase, which is conserved in plants. GWN1 negatively regulates grain length and weight by regulating cell proliferation in spikelet hulls. We also found that GWN1 negatively influenced grain number by influencing secondary branch numbers and finally increased plant grain yield. The GWN1 gene was highly expressed in inflorescences and its encoded protein is located at the cell membrane and cell wall. Moreover, we identified three haplotypes of GWN1 in the germplasm. GWN1 hap1 showing longer grain, has not been widely utilized in modern rice varieties. In summary, GWN1 played a very important role in regulating grain length, weight and number, thereby exhibiting application potential in molecular breeding for longer grain and higher yield.