Genetic, Physical and Comparative Mapping of the Powdery Mildew Resistance Gene Pm21 Originating from Dasypyrum villosum

Abstract

<i>Pm21</i>, originating from wheat wild relative <i>Dasypyrum villosum</i>, confers immunity to all known races of <i>Blumeria graminis</i> f. sp. <i>tritici</i> (<i>Bgt</i>) and has been widely utilized in wheat breeding. However, little is known on the genetic basis of the <i>Pm21</i> locus. In the present study, four seedling-susceptible <i>D. villosum</i> lines (DvSus-1 ∼ DvSus-4) were identified from different natural populations. Based on the collinearity among genomes of <i>Brachypodium distachyon, Oryza</i>, and <i>Triticeae</i>, a set of 25 gene-derived markers were developed declaring the polymorphisms between DvRes-1 carrying <i>Pm21</i> and DvSus-1. Fine genetic mapping of <i>Pm21</i> was conducted by using an extremely large F₂ segregation population derived from the cross DvSus-1/DvRes-1. Then <i>Pm21</i> was narrowed to a 0.01-cM genetic interval defined by the markers 6VS-08.4b and 6VS-10b. Three DNA markers, including a resistance gene analog marker, were confirmed to co-segregate with <i>Pm21</i>. Moreover, based on the susceptible deletion line Y18-S6 induced by ethyl methanesulfonate treatment conducted on Yangmai 18, <i>Pm21</i> was physically mapped into a similar interval. Comparative analysis revealed that the orthologous regions of the interval carrying <i>Pm21</i> were narrowed to a 112.5 kb genomic region harboring 18 genes in <i>Brachypodium</i>, and a 23.2 kb region harboring two genes in rice, respectively. This study provides a high-density integrated map of the <i>Pm21</i> locus, which will contribute to map-based cloning of <i>Pm21</i>.