| Powdery mildew, caused by Blumeria graminis f.sp. tritici, is one of the most important wheat diseases in the worldwide. Powdery mildew resistance gene of wheat is fundamental to prevention of this disease. Therefore, it's significant to mine novel powdery mildew resistance gene resoueces. Aegilops tauschii is the D genome progenitor of hexaploid wheat and thus an essential resource for wheat improvement. Genetic analysis indicated that a single dominant gene was responsible for the resistance of Y2280 using a F2 segregation population generated by the cross of resistant parent Y2280 and susceptible parent Y2282. The gene was assigned to the chromosome 5DL of Aegilops tauschii by bulk segregation analysis using molecular markers. Genetic linkage analysis indicated that 8 microsatellite markers (Xcfd266, Xgwm583, Xgwm639, Xcfd57, Xgwm174, Xcfd26, Xwmc289, and Xbarc320) were linked to the resistant gene. The most closely linked marker was Xcfd26 and Xwmc289, whose genetic distances were 10.9 and 19.3cM to resistant gene respectively. To narrow the marker interval of the resistant gene, bin-mapped EST of Chinese Spring chromosome 5DL were utilized as query to search the D genome draft sequence (unpublished) and the SNP clusters of the parents generated by the second generation sequencing technology, finally, 23 linked SSR, 32 linked SNP and 1 STS new markers were developed. The powdery mildew resistance gene was restricted between markers d39 and d69 whose genetic distance was shorten to 12.9cM. Study of comparative genomics revealed the corrosion of the colinearity of the resistance gene locus with Brachypodium and rice. Only very weak colinearity was found with rice chromosome 6, 7, 2, 4, 9 and with Brachypodium chromosome 1, 3, 5, which indicated that it was difficult to perform map-based cloning by comparative genomics method. Within the corresponding marker interval of the genetic map of Aegilops tauschii published by Luo et al., no extra markers between marker BF478964 (85.06cM) and marker Xgdm153 (102.72cM) were available. The above factors brought great difficulties to develop more efficient markers for fine mapping this powdery mildew resistance gene PmY2280.The transfer of mitochondria DNA into the nucleus is beneficial to understand the evolution of wheat. The assembly of a 1.3Mb size region of the wheat genome has provided the opportunity to study a recent nuclear mitochondrial DNA insertion (NUMT). In the present study we have studied two bacterial artificial chromosomes (BACs), characterized a 52-kb NUMT segment from the tetraploid and hexaploid wheat BAC libraries. The conserved orthologous NUMT regions from tetraploid and hexaploid wheat Langdon and Chinese Spring shared identical gene haplotypes even though mutations (insertions, deletions and substitutions) had occurred. The 52-kb NUMT was present in hexaploid variety Chinese Spring but absent in variety Hope by sequence comparison of their corresponding region. Amplifying the NUMT junctions using a set of the wheat materials including diploid, tetraploid and hexaploid lines, showed that none of the diploid wheats carried the region and only some tetraploid and hexaploid wheats were positive for the NUMT. Age estimating of the NUMT displayed the mean ages of Langdon NUMT and Chinese Spring NUMT were 378000 and 416000 years ago, respectively. Reverse transcription PCR and sequencing of nad7 gene showed 28 C→U RNA editing sites and 4 partial editing sites, and SNPs between the nuclear and mitochondrial nad7 gene which were same as the cDNA sequences. These results indicated that the expressed nad7 gene were derived from the mitochondria genome but the nucleus. |
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