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Mapping, Cloning and Functional Analysis of TGW3, a Major QTL that Negatively Modulates Grain Length and Weight in Rice

Source: China National Rice Research Institute

Grain weight, one of the most important components of rice yield, is usually measured by 1000-grain weight and determined by grain length, grain width and grain thickness. Cloning and functional characterization of a small number of relative genes/QTLs has greatly strengthened our understanding of seed development and rice yield. However, the underlying molecular mechanisms remain largely elusive.
Recently, researchers from China National Rice Research Institute (CNRRI) of Chinese Academy of Agricultural Sciences (CAAS) and Institute of Botany of Chinese Academy of Sciences (CAS) have reported that the dissection of grain size-related quantitative trait locus (QTL) compositions in a genetic population of recombinant inbreed lines (RILs) derived from the super large grain accession Jizi-1560 (JZ1560) crossed with the small-grain cultivar Huanghuazhan (HHZ) widely cultivated in Southern China. Using a high-resolution genetic map constructed with 18,194 nucleotide polymorphic SNP derived from SLAF-seq, the researchers identified more than 40 QTLs for grain length, width, weight, and yield per plant that reoccurred in two normal rice-grown seasons, most of which have not yet been cloned. The results were also confirmed by PCR genotyping of the RILs and QTL analysis. Furthermore, the researchers extended their efforts to map-based cloning of a novel QTL for thousand grain weight on the long arm of chromosome 3 (TGW3) that altered grain length and weight. Transgenic plants with overexpression of a viable candidate LOC_Os03g62500 that encodes a GSK3/SHAGGY-like kinase reduced grain size, while down-regulation and/or CRISPR/Cas9-mediated gene edition of the gene bore enlarged grain, suggesting that TGW3 exerts negative regulation of grain size. Therefore, the findings inform on the genetic architecture of a super large grain and uncover a novel mechanism of grain size regulation.

This study was supported by grants from the National Natural Science Foundation of China (Grant No.: 91435113, 31371605), National Program on Key Basic Research Project (973 Project, 2014CB943404) and Chinese High-yielding Transgenic Program (Grant No.: 2016ZX08001-004). The research findings have been published online in Molecular Plant Journal on March 7th (DOI: 10.1016/j.molp.2018.03.007). More details are available on the link below:
By Ying Jiezheng