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Keywords:

  • Arabidopsis lyrata;
  • Arabidopsis thaliana;
  • Golovinomyces;
  • orthologue;
  • population structure;
  • resistance;
  • RPW8;
  • selection

Summary

  • • 
    It is not clear to what extent the orthologues of genes that are adaptively important in one species also contribute to adaptive variation in others. Here, we examine Arabidopsis lyrata to assess the functional and evolutionary significance of natural variation in an orthologue of the gene RPW8 known to be a major determinant of powdery mildew resistance in Arabidopsis thaliana.
  • • 
    We assessed the sequence variation at RPW8 and the associated resistance reaction in populations of A. lyrata ssp. petraea. Neutrality tests were performed to understand the importance of local adaptation in maintaining variation at the locus.
  • • 
    Highly truncated RPW8 proteins were frequent in all populations and were associated with an increased risk of susceptibility. Haplotypes encoding full-length proteins were highly significantly associated with resistance. There were no signatures of selection at the species-wide level, but some evidence for positive selection in two populations.
  • • 
    RPW8 in A. lyrata appears to have a role in powdery mildew resistance, similar to its orthologue in A. thaliana. Unlike A. thaliana, A. lyrata contains a genetic component that can act independently of RPW8 to confer resistance to powdery mildew pathogens. Infrequent local selective sweeps may favour different alleles in different populations, and thereby contribute to the maintenance of species-wide variation at the locus.