Fine Mapping Of QHD8-1, A QTL Controlling The Late Heading Date In Rice (Oryza Sativa L.)

Rice is one of the importance cereal crop and the model species of monocots. Heading date (HD) is one of the importance agronomic (Yield, plant height and heading date) traits of rice. The HD of rice cultivar affects its cultivation areas and seasonal adoptability, which has been received the extensive attention of breeders for so long. Therefore, detailed understanding heading date's genetic law is significant for rice breeding practice and has the broad application prospect. At the same time, the rice's heading date gene is similar to dicotyledonous plant's florescence gene which regulates plants from the vegetative growth to the reproductive growth and also a focus in the developmental biology research in recent years.The single segment substitution lines (SSSLs) were perfect materials for analysis of gene especially for QTL. Developing the SSSLs can not only search and use the new gene resource, greatly improve veracity and accuracy of QTL mapping, but also can get those discontinuous segment together such as identify of gene, gene mapping, maker-assisted selection and breeding. Additional, using the SSSLs can achieve the development of span mode of plant molecular breeding from utilizing single gene to synthetically exploiting genome, whereas, it can accumulate abundant gene resource for gene converge breeding engineering. A library consisting of 1,230 single segment substitution lines (SSSLs) in the same genetic background of an elite rice variety Huajingxian74 (HJX74) was evaluated for heading date (HD). From this library, the SSSL W06-26-35-1-5-2 with the substituted interval of PSM152-PSM154-PSM155-RM25-RM547-RM72-RM404 was found having a gene, which performed stable and late heading in the different environments of Shandong and Hainan provinces. To map the gene governing heading date, the SSSL W06-26-35-1-5-2 was crossed with the recipient HJX74 to develop an F2 segregating population. The distribution of late and early heading plants in this population fitted a segregation ratio of 3:1, indicating the late heading was controlled by a dominant gene. The gene locus for heading date was tentatively designated as qHD8-1. Using a random sample of 460 individuals from the F2 population, the qHD8-1 was narrowed down to a region flanking by two SSR markers PSM155 and RM547. For fine mapping of qHD8-1, a large F2:3 segregating population of 3,000 individuals were developed from F2 plants heterozygous in the PSM155-RM547 region. Recombinants analysis further mapped qHD8-1 to an interval of region 26-kb with markers RM22492 and P23 bounded on the left and right sides, respectively. Sequence analysis of this 26-kb fragment revealed that it contains five putative open reading frames (ORFs), which were regrarded as candidates of qHD8-1. These results will be useful in cloning of the qHD8-1 gene and establishing a basis for molecular marker assisted breeding.