Gene Mapping Of Small-grain Mutants Sgr1 In Rice

The utilization of rice heterosis has made a great contribution to food security in China.However,with the fast economic development of our country,the rural labor force is migrating rapidly into cities.As the high labor intensity and production costs,traditional hybrid rice seed production technology system has become a technical bottleneck restricting the development of hybrid rice,and the technology of mechanized hybrid rice seed production charactered by light type and efficiency has become the main direction of hybrid rice.Rice grain size is an important agronomic character that affects rice yield,and taking advantage of the difference in grain size between parents of hybrid rice is one of the approaches and strategies to realize hybrid rice mechanized seed production.As the best strategy,to study the recessive traits of small-grain parent and breed with large-grain parent can meet the requirements of mechanical seed sorting and also has no affection on yield of a hybrid combination due to the small grain weight.The study of rice small recessive genetic mutants will lay the theoretical base for revealing the molecular mechanism of rice grain growth and development,cultivating rice small grain sterile lines and realizing the mechanization of hybrid rice seed production.In this paper,the genetic rules and related genes of small grain traits was studied,basing on the natural small-grain mutant sgr1（small grain rice 1）of indica variety 2338-357.The analysis of phenotypes,gene mapping cloning,and preliminary study of gene function were carried out to promote the application of recessive small-grain traits in hybrid rice seed production.The main results are as follows:1.Compared with the wild type 2338-357,the mutant sgr1 showed the shorter straw from seedling stage.At maturity,the characteristics such as dark green leaf,erect panicle type,tight grain setting and small round grains were showed besides short straw,with a 1000-grain weight of14.36g,a grain length of 5.87mm and a grain width of 2.34mm.2.Genetic analysis indicated that the mutant phenotype of sgr1 was controlled by a single recessive gene.With constructing F₂ genetic mapping population through hybridization between sgr1 and large-grain japonica variety IRTA129,the gene sgr1 was located between SSR markers RM18384 and RM18432 on rice chromosome 5.Further fine mapping was conducted by expanding the mapping population,and the gene sgr1 was located in physical interval of 44.8kb between marker In Del17 and InDel20.In this physical interval,there is a known gene RGA1（D1）（Os05g0333200）,which is annotated as small grain dwarf gene of rice and encodes for heterotrimer G proteinαsubunit.Genome sequencing indicated that there were three AAG base deletions on the exon 11 of gene D1 of the mutant sgr1,which resulting in the deletion of an encoded lysine.3.Four independent functional complementary lines were obtained through the verification of transgenic functional complementarity.The total DNA of transgenic plants was analyzed by PCR using the untransformed mutant sgr1 as the control,and gene D1 integration was found in all of them.