Recent emergence of the wheat Lr34 multi-pathogen resistance: insights from haplotype analysis in wheat, rice, sorghum and Aegilops tauschii
Spontaneous sequence changes and the selection of beneficial mutations are driving forces of gene diversification and key factors of evolution. In highly dynamic co-evolutionary processes such as plant-pathogen interactions, the plant’s ability to rapidly adapt to newly emerging pathogens is paramount. The hexaploid wheat gene Lr34, which encodes an ATP-binding cassette (ABC) transporter, confers durable field resistance against four fungal diseases. Despite its extensive use in breeding and agriculture, no increase in virulence towards Lr34 has been described over the last century. The wheat genepool contains two predominant Lr34 alleles of which only one confers disease resistance. The two alleles, located on chromosome 7DS, differ by only two exon-polymorphisms. Putatively functional homoeologs and orthologs of Lr34 are found on the B-genome of wheat and in rice and sorghum, but not in maize, barley and Brachypodium. In this study we present a detailed haplotype analysis of homoeologous and orthologous Lr34 genes in genetically and geographically diverse selections of wheat, rice and sorghum accessions. We found that the resistant Lr34 haplotype is unique to the wheat D-genome and is not found in the B-genome of wheat or in rice and sorghum. Furthermore, we only found the susceptible Lr34 allele in a set of 252 Ae. tauschii genotypes, the progenitor of the wheat D-genome. These data provide compelling evidence that the Lr34 multi-pathogen resistance is the result of recent gene diversification occurring after the formation of hexaploid wheat about 8,000 years ago.
KeywordsSorghum Powdery Mildew Leaf Rust Hexaploid Wheat Stripe Rust
We are indebted to the skilled technical support provided by Libby Viccars and Sutha Chandramohan. We thank Dr. Sally Norton from the Australian Tropical Grains Germplasm Centre for providing seeds of Sorghum propinquum and Dr. Joanna Risk from CSIRO Plant Industry, Canberra, for critically reviewing the manuscript. This work was supported by the Grains Research and Development Corporation grant #CSP000063, Australia, an Advanced Investigator grant of the European Research Council (ERC-2009- AdG 249996, Durableresistance), the Swiss National Science Foundation grant 3100A-127061 and a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (PIOF-GA-2009-252731, Dures).
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