Fine-mapping And Gene Cloning Of QGL-3.2 For Rice Grain Length

Carbohydrates are the main energy source of human life activities,and staple food is the main body for human beings to obtain carbohydrates.Rice（Oryza sativa L.）is the most important staple food crop in Asian countries.The main yield components of rice include panicle number,grains per panicle and grain weight.Grain weight is also determined by grain shape,including grain length,grain width and grain thickness.Grain shape also affects the appearance quality of rice.Therefore,the genetic study of grain shape has a great significance for the improvement of rice varieties.In this study,a QTL qGL-3.2 affecting the grain length of rice was mapped using the chromosome segment substitution lines（CSSLs）constructed by Japonica rice Sasanishiki as the recipient parent and Indica rice Habataki as the donor parent.Through fine mapping and gene editing,the candidate genes of qGL-3.2 were preliminarily determined.The main results are as follows:1.Through QTL mapping of the CSSL population,a QTL named qGL-3.2 controlling grain length locating on chromosome 3 was repeatedly detected.2.S1422 is a single segment introgression line containing qGL-3.2,and its grain length is shorter than the parent Sasanishiki.According to the electron microscope scaning of the hull of mature grains,the number of epithelial cells between SL422 and Sasanishiki showed no difference,but the longitudinal length of SL422 cells is shorter than Sasanishiki.Thus,shortened grain length of SL422 was caused by limitated elongation of hull epithelial cells,but not the cell proliferation process.3.The CSSL SL422 containing qGL-3.2 was backcrossed and selfed with the recurrent parent Sasanishiki to construct a population for fine mapping of qGL-3.2.Finely,qGL-3.2 was mapped to a 23.1 kb region in which contains three canidiate genes:ORF-A,ORF-B and most of the upstream sequence of ORF-A.4.CRISPR/Cas9 was used to edit the candidate genes ORF-A,ORF-B and ORF-C respectively.The results showed that the mutation of ORF-A or ORF-B increased the grain length,while the grain length of the mutants of ORF-C was not significantly changed.Therefore,both of ORF-A and ORF-B may be candidate genes for qGL-3.2,which jointly regulate grain length.