Origin and maintenance of a broad-spectrum disease resistance locus in Arabidopsis.

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TitleOrigin and maintenance of a broad-spectrum disease resistance locus in Arabidopsis.
Publication TypeJournal Article
Year of Publication2004
AuthorsXiao, S, Emerson, B, Ratanasut, K, Patrick, E, O'Neill, C, Bancroft, I, Turner, JG
JournalMol Biol Evol
Volume21
Issue9
Pagination1661-72
Date Published2004 Sep
ISSN0737-4038
KeywordsAmino Acid Sequence, Arabidopsis, Arabidopsis Proteins, Brassica, Evolution, Molecular, Gene Duplication, Genes, Plant, Genome, Plant, Molecular Sequence Data, Multigene Family, Phylogeny, Plant Diseases, Sequence Homology, Amino Acid
Abstract

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, which suggests a recent origin. In addition to RPW8.1 and RPW8.2, the RPW8 locus contains three homologs 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 analyzed 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 locus contains three genes and is present in both B. oleracea and B. rapa, and the other locus contains a single gene and is detected in B. rapa only. The Brassica homologs 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 MYA. Examination of the sequence polymorphism of 32 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.

DOI10.1093/molbev/msh165
Alternate JournalMol. Biol. Evol.
PubMed ID15155802