Comparative Genomics Analysis and Constructing EST Markers Linkage Map of Powdery Mildew Resistance Gene <I>pm42</I> in Wheat

Constructing fine genetic linkage map of target gene provides a starting point for map-based cloning. Fine genetic mapping of functional genes in wheat has benefited greatly from comparative genomics analysis. The genome sequences of rice and Brachypodium distachyon provide powerful tools for comparative genomics analysis and fine genetic mapping of target gene in wheat. In the present study, comparative genomics analysis using wheat-Brachypodium-rice genomic colinearity showed that genomic region containing pm42 in wheat 2BS was orthologous to Brachypodium chromosome 1 and rice chromosome 3. Two EST-SSCP markers, CD452782 and BF201235, three EST-STS markers, CJ674042, EB513371, and CV771633, linked to pm42 were developed and an EST marker-based genetic linkage map of pm42 was constructed. CJ674042, BF201235, CD452782, and CV771633 were distal to pm42 with genetic distances of 1.9, 12.0, 19.7, and 25.7 cM, respectively. EB513371 was proximal to pm42 with a genetic distance of 14.6 cM. An integrated high-density comparative genomics genetic linkage map of pm42 was constructed and the powdery mildew resistance gene was mapped in a 3.3 cM interval orthologous to 66 kb and 69 kb genomic regions in Brachypodium chromosome 1 and rice chromosome 3, respectively, providing useful information for the fine mapping, molecular assisted selection and gene pyramiding of pm42.