Fine Mapping Of Heading Date Gene TaHdM605 In Hexaploid Wheat(Triticum Aestivum L.)

The optimum flowering(heading) time is essential for sustainable productivity and high yield potential of crops, therefore, molecular characterization of wheat flowering regulatory genes can not only enhance our understanding of the mechanisms underlying wheat flowering regulation, but also benefit wheat breeding by improving the flowering phenotype. Gene fine mapping is cornerstone of positional gene cloning. Here we present fine mapping wheat heading date gene Ta Hd M605 by developing new molecular markers through comparative genomics and draft genome sequences of Aegilops tauschii.Wheat late heading mutant M605 was screened from wheat variety Yan Zhan 4110(YZ4110) EMS mutant library and a recessive gene was identified in this mutant. In order to map the late heading date gene Ta Hd M605, a cross between the M605 and the early heading variety Spring 47 from CIMMITY was made and Ta Hd M605 was mapped on 3DL by the public SSR markers. Subsequently, the sequences of franking markers barc42 and cfd152 were used to blast the genome sequences of rice, sorghm, barley and Brachypodium. The target gene was anchored on the region of LOC_ Os01g66190- LOC_ Os01g67360 in rice, Sb03g042010-Sb03g042770 in sorghm, 480Mb-510 Mb in barley chromosome 3H and Bradi2g57170-Bradi2g57710 in Brachypodium, respectively. The collinearity among the species was good on micro level. One thousand forty six new SSR markers were developed based on the comparative information and 8 markers linked to target gene were found. Among these markers, marker M310 had 0.8c M distance to the target gene. When we further did the comparative analysis among the species, we found that the micro collinearity of the target region was poor. Therefore, the recent published chromosome 3B sequence and Aegilops tauschii draft genome sequence were employed to develop new markers. Twelve markers were identified to be linked with the target gene, and marker M35 was co-segregated with Ta Hd M605. To fine mapping Ta Hd M605, the mapping population size was enlarged, including 3228 F2 individuals, 1468 homozygous recessive individuals from sub-populations, and a fine map of Ta Hd M605 was drawn and the genotypes of the recombinants were identified. Finally, the heading date gene Ta Hd M605 was anchored between two markers M310 and M27. M310 had 2 recombinant plants, M27 had 1 recombinant plant, and M35 was co-segregated with Ta Hd M605.Marker M35 was harbored on the scaffold1510. Sequence analysis of this scaffold and adjacent scaffolds was performed by blast database of NCBI and TREP, 54 genes were identified after combining the results of gene prediction, repetitive sequence and EST analysis, and gene expression data. Among them, 15 possible genes were first selected to develop SNP markers. Sixteen linked SNP loci were identified and the SNP validation was underway.In addition, the combination of the high-density genetic map of Aegilops tauschii built by our lab and phenotypes of the heading date from the mapping population, a new heading date major QTL located on the region bin 77 to bin 78 of chromosome 7D was identified in Aegilops tauschii. The contribution rate of this QTL was up to 21.73%. Further, the sequences from bin77 and bin78 were used to blast rice genome sequence, the collinearity of the target region between Aegilops tauschii and rice was found to be very poor. It meant that only wheat genome sequence itself could be very helpful in developing new markers to narrow down the distance to the target gene.