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.

Agriculture and Food Commonwealth Scientific and Industrial Research Organization GPO Box 1700 Canberra ACT 2601 Australia

Centre of the Region Haná for Biotechnological and Agricultural Research Institute of Experimental Botany of the Czech Academy of Sciences Šlechtitelů 31 Olomouc 779 00 Czech Republic

Department of Plant and Microbial Biology University of Zurich Zollikerstrasse 107 Zürich 8008 Switzerland

John Innes Centre Norwich NR4 7UH UK

OT Gatersleben Leibniz Institute of Plant Genetics and Crop Plant Research Corrensstr 3 Stadt Seeland D 06466 Germany

School of Life and Environmental Sciences Plant Breeding Institute University of Sydney 107 Cobbitty Road Cobbitty NSW 2570 Australia

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Dissection of a rapidly evolving wheat resistance gene cluster by long-read genome sequencing accelerated the cloning of Pm69

Updated guidelines for gene nomenclature in wheat