Recently, a paper entitled “Natural variation in the promoter of TGW2 determines grain width and weight in rice” was published online by New Phytologist. In the paper, CNRRI researchers report the cloning and characterization of a new semidominant QTL TGW2 for grain width and weight. Findings provide new insights into the genetic mechanism underlying grain morphology and grain weight, and uncover a promising gene for improving rice yield.

Using a recombinant inbred line population composed of 132 lines derived from cross between indica rice variety 93-11 and small-grain cultivar PA64s, three QTLs for grain width along with two QTLs for grain weight were identified. Through investigation into large scale BC4F2 population, map-based cloning of a QTL related to grain width and weight, TGW2 was performed, which encodes a cell number regulator (OsCNR1). A single nucleotide polymorphism (SNP) variation at upstream of TGW2 is responsible for its different transcriptional expression level, leading to alteration in grain width and weight by influencing cell proliferation and expansion in glumes. TGW2 interacts with KRP1, a regulator of plant cell cycle, to negatively regulate grain width and weight. Field test showed that the allele of tgw^293-11 increases the grain yield by 12.3% than TGW2^PA64s without affecting other agronimic traits. Genetic diversity analysis of TGW2 in 141 rice accessions revealed it as a breeding target in a selective sweep region, indicating that this gene is under selection during domestication.

The research was supported by the National Key Research and Development Program of China (2016YFD0100400), National Natural Science Foundation of China (Grant Nos 31471167, 91735304, 31671761 and 31901481), and Science, Technology and Innovation Commission of Shenzhen Municipality (JCYJ20170303154506881).