Genetic Analysis And Fine-mapping Of A Late Heading-date With Dwarfing Mutant In Rice (Oryza Sativa L.)

Heading date is the one of the most important agronomic trait in rice, determining rice varieties adaptability to different areas and seasons. It is also paid much attention by rice breeders. Photosensitivity, temperature and vegetative growth of these three factors determine the length of heading date. Various combinations of the three factors result in not onlydiversity of the heading date, but also its complex genetic characteristics. It is necessary to identify some new mutants with various heading dates for genetic ananlysis, owing to the unclear complex regulatory mechanism of heading date. On the other hand, heading date is closely related to the formation of yield, so the clarifying of the molecular mechanism of control the heading date length will be beneficial to further improvement the potential of rice yield.A new heading date mutant (late heading date with dwarfing, lhdd) derived from a japonica cultivar Nipponbare with tissue culture was used in this study. lhdd showed the phenotypes of late heading date with dwarfing. We used map-based cloning method to map the gene. The study shed light on the molecular mechanism of control flowering in rice. The results of our studies are as follows:1) The mutant and their generations all showed the late heading date with dwarfing trait that can be inherited stably.2) Comparing to the wild type Nipponbare, lhdd showed a 20-days delay in heading date and accompanied by a number of pleiotropic phenotypes, such as, reduced plant height, panicle smeller, low percentage of seed-setting and the tiller number increased.3) The analysis of endospermα-amylase activity inferred the dwarfing in lhdd mutant is independent of GA synthesis or signal transduction.4) Photoperiod treatment assay results showed that when lhdd was grown in Fuyang city, Zhejiang province, the heading date of the mutant was twenty days late compared with the wild-type; while cultivated in Ningshui city, Hainan province, the heading date delayed thirteen days compared with the wild-type. The results indicated that the heading date of the lhdd mutant planted in SD was seven days earlier when than that in LD.5) To identify whether the lhdd mutant was controlled by a single gene, genetic analysis on reciprocal crosses between lhdd and japonica cultivars NPB, CJ06 and ZH11 were conducted, the results showed that lhdd was a recessive mutant, based on the individuals of the F2 segregation population, all the ratio of normal heading date and late heading date individuals fit into 3:1 (χ2<χ20.05,1=3.84), indicating that the lhdd mutant was controlled by a single recessive gene.6) 184 F2 mutagenic individuals derived from lhdd and TN1 cross were screened for the primary mapping, and the LHDD was located on the long arm of chromosome 1 between the two STS markers WY3 and WE20. Then the candidate region was delimited to a 40 kb physical distance, the forecast websites predicted that there are five open reading frames in the region.