FGW1, a protein containing DUF630 and DUF632 domains, regulates grain size and filling in Oryza sativa L.

Abstract Grain filling is a crucial trait that influences grain size and quality in cereal crops. However, the molecular mechanisms that regulate endosperm development remain elusive. In this study, we characterize a filling-defective and grain width mutant fgw1, which increased rice seed width mainly by influencing cell division and expansion in the glumes. Sucrose contents were higher, whereas starch contents were lower, in the fgw1 mutant during the grain-filling stage, which resulted in inferior endosperm of opaque, white appearance with loosely packed starch granules. Map-based cloning revealed that FGW1 encoded a protein containing DUF630/DUF632 domains, localized in the plasma membrane with preferential expression in the panicle. RNA interference of FGW1 resulted in increased grain width and weight, whereas overexpression of FGW1 led to a slightly narrower grain with better grain quality. A yeast two-hybrid assay showed that FGW1 can directly interact with the 14-3-3 protein GF14f, and bimolecular fluorescence complementation verified that the site of interaction was the membrane, and the mutated FGW1 protein failed to interact with GF14f. The expression of GF14f was down-regulated in fgw1, and the activities of AGPase, StSase and SuSase in the endosperm of fgw1 increased significantly just as those of reported GF14f-RNAi. Transcriptome analysis indicated that FGW1 also regulates cellular processes and carbohydrate metabolism. Therefore, this study showed that FGW1 regulated grain formation by the GF14f pathway.