title: Intragenic recombination and diversifying selection contribute to the evolution of downy mildew resistance at the RPP8 locus of Arabidopsis.
abstract: Pathogen resistance (R) genes of the NBS-LRR class (for nucleotide binding site and leucine-rich repeat) are found in many plant species and confer resistance to a diverse spectrum of pathogens. Little is known about the mechanisms that drive NBS-LRR gene evolution in the host-pathogen arms race. We cloned the RPP8 gene (for resistance to Peronospora parasitica) and compared the structure of alleles at this locus in resistant Landsberg erecta (Ler-0) and susceptible Columbia (Col-0) accessions. RPP8-Ler encodes an NBS-LRR protein with a putative N-terminal leucine zipper and is more closely related to previously cloned R genes that confer resistance to bacterial pathogens than it is to other known RPP genes. The RPP8 haplotype in Ler-0 contains the functional RPP8-Ler gene and a nonfunctional homolog, RPH8A. In contrast, the rpp8 locus in Col-0 contains a single chimeric gene, which was likely derived from unequal crossing over between RPP8-Ler and RPH8A ancestors within a Ler-like haplotype. Sequence divergence among RPP8 family members has been accelerated by positive selection on the putative ligand binding region in the LRRs. These observations indicate that NBS-LRR molecular evolution is driven by the same mechanisms that promote rapid sequence diversification among other genes involved in non-self-recognition.
authors.affiliation: Department of Biology, C.B. 3280 Coker Hall, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: McDowell
authors.forename: M
authors.initials: M
authors.lastname: Dhandaydham
authors.forename: T A
authors.initials: TA
authors.lastname: Long
authors.forename: M G
authors.initials: MG
authors.lastname: Aarts
authors.forename: S
authors.initials: S
authors.lastname: Goff
authors.forename: E B
authors.initials: EB
authors.lastname: Holub
authors.forename: J L
authors.initials: JL
authors.lastname: Dangl
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000382:microbiology*; D001483:Base Sequence; D002874:Chromosome Mapping; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D017343:Genes, Plant; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D009868:Oomycetes / Q000472:pathogenicity*; D010641:Phenotype; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics; D030821:Plants, Genetically Modified; D011995:Recombination, Genetic; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins