Fine Physical and Genetic Mapping of Powdery Mildew Resistance Gene <i>MlIW172</i> Originating from Wild Emmer (<i>Triticum dicoccoides</i>)

<div><p>Powdery mildew, caused by <i>Blumeria graminis</i> f. sp. <i>tritici</i>, is one of the most important wheat diseases in the world. In this study, a single dominant powdery mildew resistance gene <i>MlIW172</i> was identified in the IW172 wild emmer accession and mapped to the distal region of chromosome arm 7AL (bin7AL-16-0.86-0.90) via molecular marker analysis. <i>MlIW172</i> was closely linked with the RFLP probe <i>Xpsr680</i>-derived STS marker <i>Xmag2185</i> and the EST markers <i>BE405531</i> and <i>BE637476</i>. This suggested that <i>MlIW172</i> might be allelic to the <i>Pm1</i> locus or a new locus closely linked to <i>Pm1</i>. By screening genomic BAC library of durum wheat cv. Langdon and 7AL-specific BAC library of hexaploid wheat cv. Chinese Spring, and after analyzing genome scaffolds of <i>Triticum urartu</i> containing the marker sequences, additional markers were developed to construct a fine genetic linkage map on the <i>MlIW172</i> locus region and to delineate the resistance gene within a 0.48 cM interval. Comparative genetics analyses using ESTs and RFLP probe sequences flanking the <i>MlIW172</i> region against other grass species revealed a general co-linearity in this region with the orthologous genomic regions of rice chromosome 6, <i>Brachypodium</i> chromosome 1, and sorghum chromosome 10. However, orthologous resistance gene-like RGA sequences were only present in wheat and <i>Brachypodium</i>. The BAC contigs and sequence scaffolds that we have developed provide a framework for the physical mapping and map-based cloning of <i>MlIW172</i>.</p></div

Mapped wheat EST markers and ortholgous gene pairs among <i>Brachypodium</i>, rice and sorghum

<p>Mapped wheat EST markers and ortholgous gene pairs among <i>Brachypodium</i>, rice and sorghum</p

PCR amplification patterns of the markers <i>WGGC4656, WGGC4657, WGGC4658, WGGC4659, WGGC4660, WGGC4661, WGGC4662, WGGC4663, WGGC4664</i>, and <i>WGGC4665</i> in 8% non-denatured polyacrylamide gels.

<p>M: 2kb DNA marker. Lanes 1 and 2 are IW172 and Mo75, respectively, lanes 3–6 represent homozygous resistant plants, lanes 7–10 represent homozygous susceptible plants, and lanes 11–14 represent heterozygous resistant plants.</p

Genetic and comparative genomics linkage map of powdery mildew resistance gene <i>MlIW172</i> derived from wild emmer.

<p><b>A: </b><i>MlIW172</i> physical bin map. <i>MlIW172</i> was mapped to the distal bin 7AL16-0.86-0.90. <b>B:</b> Preliminary <i>MlIW172</i> genetic map on wheat chromosome arm 7AL with genetic distances in cM shown on the left, markers shown on the right. <b>C: </b><i>MlIW172</i> high-resolution genetic map on wheat 7AL arm with genetic distances in cM shown on the left, EST-STS, EST-SSR and SSR markers shown on the right. Molecular markers that were previously assigned to the 7A wheat deletion bin map (<b>A</b>) are connected to the physical map with solid lines. The <i>MlIW172</i> locus is in red and underlined. The markers which served as anchors, establishing colinearity between the <i>MlIW172</i> genetic map and the sequences of <i>Brachypodium</i>, rice and sorghum, are connected to the <i>Brachypodium</i> gene with solid lines. <b>D:</b> The <i>MlIW172</i> orthologous genomic region on <i>Brachypodium</i> chromosome 1 (150kb) with orthologous genes shown on the right. The four genes in green represent the RGA cluster. <b>E:</b> The <i>MlIW172</i> orthologous genomic region on rice chromosome 6 (85.8kb) with orthologous genes shown on the right. <b>F:</b> The <i>MlIW172</i> orthologous genomic region on sorghum chromosome 10 (138.9kb) with orthologous genes shown on the right.</p

Physical map of the BAC contigs and scaffolds flanking the <i>MlIW172</i> locus anchored to the high-resolution genetic map.

<p>The approximate physical locations of all the newly designed markers are given on the BAC contigs or scaffolds.</p

Genetic analysis of the powdery mildew resistance gene <i>MlIW172</i>

<p>A, H, B represent homozygous resistant, heterozygous resistant and homozygous susceptible, respectively.</p

Integrative views of the <i>MlIW172</i> gene loci with other previously published <i>Pm</i> genes on chromosome arm 7AL.

<p>The loci can be classified into three groups (Group I; Group II; Group III) based on their order and genetic distance to markers <i>Xwmc525</i> and <i>Xgwm344</i>.</p

EST-STS, EST-SSR and SSR markers linked to powdery mildew resistance gene <i>MlIW172</i>

<p>EST-STS, EST-SSR and SSR markers linked to powdery mildew resistance gene <i>MlIW172</i></p