A Rare Allele of GS2 Enhances Grain Size and Grain Yield in Rice

Grain size determines grain weight and affects grain quality. Several major quantitative trait loci (QTLs) regulating grain size have been cloned; however, our understanding of the underlying mechanism that regulates the size of rice grains remains fragmentary. Here, we report the cloning and characterization of a dominant QTL, GRAIN SIZE ON CHROMOSOME 2 (GS2), which encodes Growth-Regulating Factor 4 (OsGRF4), a transcriptional regulator. GS2 localizes to the nucleus and may act as a transcription activator. A rare mutation of GS2 affecting the binding site of a microRNA, OsmiR396c, causes elevated expression of GS2/OsGRF4. The increase in GS2 expression leads to larger cells and increased numbers of cells, which thus enhances grain weight and yield. The introduction of this rare allele of GS2/OsGRF4 into rice cultivars could significantly enhance grain weight and increase grain yield, with possible applications in breeding high-yield rice varieties. Grain size determines grain weight and affects grain quality. GS2, a dominant QTL, encodes Growth-Regulating Factor 4 (OsGRF4), which acts as a transcriptional regulator. A mutation in this gene at the OsmiR396c target site results in elevated transcript levels of GS2 and accumulation of GS2 leads to enlarged cell size and increased cell number, which in turn results in enhanced grain weight and yield.