MBE Advance Access published online on May 21, 2004
Molecular Biology and Evolution, doi:10.1093/molbev/msh165
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2004; all rights reserved
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1 School of Biological Sciences, University of East Anglia, NR4 7TJ, UK
* To whom correspondence should be addressed. E-mail: j.g.turner{at}uea.ac.uk.
The broad-spectrum mildew resistance genes RPW8.1 and RPW8.2 define a unique type of plant disease resistance (R) gene and so far homologous sequences have been found in Arabidopsis thaliana only, suggesting a recent origin. In addition to RPW8.1 and RPW8.2, the RPW8 locus contains three homologues of RPW8, HR1, HR2, and HR3, which do not contribute to powdery mildew resistance. To investigate whether RPW8 has originated recently, and if so the processes involved, we have isolated and analysed the syntenic RPW8 loci from Arabidopsis lyrata, and from Brassica rapa and B. oleracea. The A. lyrata locus contains four genes orthologous to HR1, HR2, HR3 and RPW8.2 respectively. Two syntenic loci have been characterized in Brassica, one contains three genes and is present in both B. oleracea and B. rapa, and the other contains a single gene and is detected in B. rapa only. The Brassica homologues have highest similarity to HR3. Sequence analyses suggested that the RPW8 gene family in Brassicaceae originated from an HR3-like ancestor gene through a series of duplications, and that RPW8.1 and RPW8.2 evolved from functional diversification through positive selection several millions of years ago. Examination of the sequence polymorphism of thirty two A. thaliana accessions at the RPW8 locus and their disease reaction phenotypes revealed that the polymorphic RPW8 locus defines a major source of resistance to powdery mildew diseases. A possible evolutionary mechanism by which functional polymorphism at the AtRPW8 locus has been maintained in contemporary populations of A. thaliana is discussed. Key Words:
RPW8, disease resistance, powdery mildew, Arabidopsis, Brassica
Original Articles
Origin and Maintenance of a Broad-Spectrum Disease Resistance Locus in Arabidopsis
2 John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK
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