A highly differentiated region of wheat chromosome 7AL encodes a <i>Pm1a</i> immune receptor that recognizes its corresponding <i>AvrPm1a</i> effector from <i>Blumeria graminis</i>
Tim Hewitt, Marion C. Müller, István Molnár, Martin Mascher, Kateřina Holušová, Hana Šimková, Lukas Kunz, Jianping Zhang, Jianbo Li, Dhara Bhatt, R. K. Sharma, Seraina Schudel, Guotai Yu, Burkhard Steuernagel, Sambasivam Periyannan, Brande B. H. Wulff, Mick Ayliffe, R. A. McIntosh, Beat Keller, Evans Lagudah, Peng Zhang
Abstract
Pm1a, the first powdery mildew resistance gene described in wheat, is part of a complex resistance (R) gene cluster located in a distal region of chromosome 7AL that has suppressed genetic recombination. A nucleotide-binding, leucine-rich repeat (NLR) immune receptor gene was isolated using mutagenesis and R gene enrichment sequencing (MutRenSeq). Stable transformation confirmed Pm1a identity which induced a strong resistance phenotype in transgenic plants upon challenge with avirulent Blumeria graminis (wheat powdery mildew) pathogens. A high-density genetic map of a B. graminis family segregating for Pm1a avirulence combined with pathogen genome resequencing and RNA sequencing (RNAseq) identified AvrPm1a effector gene candidates. In planta expression identified an effector, with an N terminal Y/FxC motif, that induced a strong hypersensitive response when co-expressed with Pm1a in Nicotiana benthamiana. Single chromosome enrichment sequencing (ChromSeq) and assembly of chromosome 7A suggested that suppressed recombination around the Pm1a region was due to a rearrangement involving chromosomes 7A, 7B and 7D. The cloning of Pm1a and its identification in a highly rearranged region of chromosome 7A provides insight into the role of chromosomal rearrangements in the evolution of this complex resistance cluster.