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

Abstract

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most important wheat diseases in the world. In this study, a single dominant powdery mildew resistance gene MlIW172 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. MlIW172 was closely linked with the RFLP probe Xpsr680-derived STS marker Xmag2185 and the EST markers BE405531 and BE637476. This suggested that MlIW172 might be allelic to the Pm1 locus or a new locus closely linked to Pm1. 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 Triticum urartu containing the marker sequences, additional markers were developed to construct a fine genetic linkage map on the MlIW172 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 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. However, orthologous resistance gene-like RGA sequences were only present in wheat and Brachypodium. The BAC contigs and sequence scaffolds that we have developed provide a framework for the physical mapping and map-based cloning of MlIW172.

Fine Mapping of Two Wheat Powdery Mildew Resistance Genes Located at the Pm1 Cluster

“…Since powdery mildew R gene MlIW172 was mapped to the same chromosomal regions as Mlm2033 – Mlm80 (Ouyang et al, 2014), markers linked to MlIW172 were also surveyed for polymorphism. WGGC4659 and WGGC4655 with Hae III digestion detected polymorphism between the resistant and susceptible bulks of the Mlm2033 and Mlm80 .…”

“…Wheat expressed sequence tags (ESTs) deposited in the NCBI (http://www.ncbi.nlm.nih.gov/nucest), T. urartu genome scaffolds (Ling et al, 2013) and survey sequence contigs of the wheat cultivar Chinese Spring (International Wheat Genome Sequencing Consortium, http://www.wheatgenome.org) that are homologous to the predicted coding DNA sequences (CDS) in the B. distachyon chromosomal region collinear to the Mlm2033 – Mlm80 interval were used for development of simple‐sequence repeat (SSR) or sequence‐tagged site (STS) markers. Additional markers were designed based on the tetraploid wheat BAC sequence LDN133‐865 (GI: 636536483) (Ouyang et al, 2014), courtesy of Dr. Zhiyong Liu of China Agricultural University. Triticum urartu sequence scaffold9207 (GI: 473888380) (Ling et al, 2013), which contains one CDS homologous to Bradi1 g29693 , was also used for marker design.…”

“…However, some of the so‐called allelic relationships might result from tight linkage of different R genes. At Pm1 , apart from Pm1a to Pm1e , PmU , Mlm2033 , Mlm80 , MlIM72 , MIAG12 , PmG16 , MlIM172 , HSM1 and PmTb7A.2 , were all mapped to the same chromosomal interval (Hsam et al, 1998; Singrün et al, 2003; Qiu et al, 2005; Yao et al, 2006; Ji et al, 2008; Maxwell et al, 2009; Ben‐David et al, 2010; Ouyang et al, 2014; Li et al, 2014; Chhuneja et al, 2012, 2015), which was subjected to recombination suppression (Neu et al, 2002). Therefore, Pm1 might represent a significant R ‐gene cluster with genes identified in wheat accessions of different ploidy levels.…”

Molecular mapping ofYrTZ2, a stripe rust resistance gene in wild emmer accession TZ-2 and its comparative analyses withAegilops tauschii

“…Comparative genomics analyses provided an effective way for wheat gene mapping. By applying comparative genomics analysis using genome sequences of Brachypodium , rice or sorghum, high-density genetic linkage maps of vernalization ( VRN ) genes (Yan et al 2003, 2004, 2006), pairing homologous 1 ( Ph1 ) (Griffiths et al 2006), grain protein content-B1 ( Gpc - B1 ) (Uauy et al 2006), yellow rust resistance gene Yr36 (Fu et al 2009), wax production gene W1 (Lu et al 2015) and powdery mildew resistance gene Pm6 (Qin et al 2011), Pm41 ( Wang et al 2014), Ml3D232 (Zhang et al 2010), MlIW170 (Liu et al 2012; Liang et al 2015), MlIW172 (Ouyang et al 2014) were constructed. The draft genome sequences of T. aestivum cv.…”

Fine mapping of powdery mildew resistance genes PmTb7A.1 and PmTb7A.2 in Triticum boeoticum (Boiss.) using the shotgun sequence assembly of chromosome 7AL

“…2013; Mwale et al 2014;Ouyang et al 2014;Zhan et al 2014;Hao et al 2015;Petersen et al 2015). Twenty-one RGA-STS, 8 SSR and 13 SNP markers were mapped to 7AL.…”