Plant mechanical strength affects lodging resistance and stress tolerance, highlighting the importance of elucidating the regulatory mechanisms underlying cell wall development. In this study, we identified a novel dwarf and brittle culm mutant, dbc3, which exhibited reduced culm mechanical strength due to a thinner secondary cell wall, irregular distribution of the sclerenchyma cells under the epidermal layer and vascular bundle cells, as well as a significant reduction in cellulose and lignin content. Map-based cloning revealed that DBC3 encodes a xylan arabinosyltransferase belonging to the GT61 family. GUS staining and qRT-PCR showed that DBC3 was expressed in all tested tissues. Yeast one-hybrid, dual-luciferase assays and EMSA demonstrated that OsMYB63 directly bound to the DBC3 promoter to activate its expression. In the osmyb63 knockout mutant, DBC3 expression was significantly reduced, accompanied by a moderate decrease in stem mechanical strength. Taken together, these findings suggest that DBC3, as a direct target gene of OsMYB63, plays an important role in regulating plant mechanical strength by modulating cell wall development.

Grain filling influences grain size and quality in cereal crops. The molecular mechanisms that regulate grain endosperm development remain elusive. In this study, we characterized a filling-defective and grain width mutant, fgw1, whose mutation increased rice seed width mainly via cell division and expansion in grains. Sucrose contents were higher but starch contents lower in the fgw1 mutant during the grain-filling stage, resulting 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 in FGW1 resulted in increased grain width and weight, whereas overexpression of FGW1 led to slightly narrower kernels and better grain filling. In a yeast two-hybrid assay, FGW1 interacted directly with the 14–3–3 protein GF14f, 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 similarly to those of a reported GF14f-RNAi. Transcriptome analysis indicated that FGW1 also regulates cellular processes and carbohydrate metabolism. Thus, FGW1 regulated grain formation via the GF14f pathway.