Gγ-protein GS3 Function in Tight Genetic Relation with OsmiR396/GS2 to Regulate Grain Size in Rice.

Manipulating grain size demonstrates great potential for yield promotion in cereals since it is tightly associated with grain weight. Several pathways modulating grain size have been elaborated in rice, but possible crosstalk between the ingredients is rarely studied. OsmiR396 negatively regulates grain size through targeting OsGRF4 (GS2) and OsGRF8, and proves to be multi-functioning. Here we showed that expression of GS3 gene, a Gγ-protein encoding gene, that negatively regulates grain size, was greatly down-regulated in the young embryos of MIM396, GRF8OE and GS2OE plants, indicating possible regulation of GS3 gene by OsmiR396/GRF module. Meanwhile, multiple biochemical assays proved possible transcriptional regulation of OsGRF4 and OsGRF8 proteins on GS3 gene. Further genetic relation analysis revealed tight genetic association between not only OsmiR396 and GS3 gene, but also GS2 and GS3 gene. Moreover, we revealed possible regulation of GS2 on four other grain size-regulating G protein encoding genes. Thus, the OsmiR396 pathway and the G protein pathway cross talks to regulate grain size. Therefore, we established a bridge linking the miRNA-transcription factors pathway and the G-protein signaling pathway that regulates grain size in rice.