Fine Mapping Of Powdery Mildew Resistance Gene MlIW172 Derived From Wild Emmer And Sequencing The 3DS Chromosome Arm Of Aegilops Tauschii

Powdery mildew,caused by Blumeria graminis f.sp.tritici(Bgt),is one of serious foliar diseases of wheat affecting grain yield and quality worldwide.So far,more than 40 wheat powdery mildew resistance loci have been identified from different chromosomes of wheat.However,the emergence of new virulent pathogen races often leads to many resistance genes losing or reducing their resistance.Identification and effective utilization of new powdery mildew resistance genes become necessary for disease resistance breeding program.Wild emmer,the progenitor of cultivated tetraploid and hexaploid wheat,rich in genetic diversity for powdery mildew resistance,can be used for genetic improvement of common wheat.In this study,wild emmer accession IW172 collected from Israel was used to cross with cultivated tetraploid durum wheat Mo75 to generate fine mapping population for powdery mildew resistance gene MlIW172.Based on the preliminary genetic mapping,a high-resolution genetic linkage map was developed with alignment to a draft physical map covering the MlIW172 region by using a combinational approach of comparative and genetic analysis of wheat EST in MlIW172 region with rice,Brachypodium distachyon and sorghum,and BAC/scaffolds sequences of Langdon BAC library,Triticum urartu genome and Chinese 7AL BAC library.The work provides a framework for map-based cloning of the MlIW172.Also,3112 MTP BAC clones of Aegilops tauschii(goatgrass),the diploid progenitor of the bread wheat D-genome,chromosome arm 3DS were sequenced,assembled and compared with Chinese Spring 3B chromosome.The main results are described as follows:1.A fine mapping population including 4192 F2 plants and its F2:3 generation of Mo75/IW172 was developed and tested for powdery mildew reaction.2.Comparative genetics analyses using ESTs sequences flanking the MlIW172 region against other grass species revealed a general co-linearity in this region with the orthologous genomic regions of rice chromosome 6,Brachypodium chromosome 1,and sorghum chromosome 10.Five EST-STS makers,XRGA-C6,XRGA-B6,WGGC4653,WGGC4654 and WGGC4655 were found to be polymorphic between the parental lines Mo75 and IW172 and resistant and susceptible bulks,and were subsequently used to construct a MlIW172 high-density linkage map.Three markers,WGGC4656,WGGC4657 and WGGC4658,closely linked to MlIW172 were developed from the BAC sequences identified from the BAC library of drum wheat cv.Langdon(LND).The CDS of the Brachypodium genes in the colinearity region of MlIW172 were used to blast the T.urartu genome scaffolds.Five SSR markers WGGC4659,WGGC4660,WGGC4661,WGGC4662 and WGGC4663 were developed from scaffold25403(333kb)and scaffold96474(61kb).Five additional polymorphic SSR markers WGGC4664,WGGC4665,WGGC4666,WGGC4667 and WGGC4668 were developed from BAC Contig841 of the Chinese Spring 7AL BACs.All the markers developed are tested in the population and intergrated into the high-resolution genetic map.The closest markers WGGC4664(WGGC4665,WGGC4668)and WGGC4659 delineate MlIW172 to an interval of 0.48 cM.3.The MTP BAC clones of Aegilops tauschii chromosome arm 3DS were sequenced with Roche 454 platform using BAC-by-BAC method.The total sequence length of the assembled BAC pools of 3DS was 382Mb.4.Comparative genomics analysis of the corresponding of different sub-genomes at different ploidy levels revealed that big gene losses and genomic rearrangement were happened during the two polyploidization event of wheat.