Variation and phylogenetic utility of the Arabidopsis thaliana Rps2 homolog in various species of the tribe Brassiceae

Our objective was to analyze the evolutionary paths of cultivated diploid B rassica species and a few related wild species (tribe Brassiceae) in relati on to Arabidopsis thaliana (tribe Arabidae), using the Rps2 sequence. Rps2 confers resistance to Pseudomonas syringae in A. thaliana. We found that si milar to Arabidopsis, the Rps2 homolog in Brassica species is present in a single copy. Primers based in the Rps2 sequence amplified Rps2 homologs fro m the other species. Maximum-parsimony analysis based on number of nucleoti de substitutions yielded a single tree, grouping the species as expected fr om other evolutionary inferences. Age of divergence between the two tribes was within the range of previous estimates. Indels in the different sequenc es were also useful for distinguishing some of the species. The Rps2 gene i s a useful phylogenetic tool for more comprehensive studies of the species of Brasicaceae. (C) 2000 Academic Press.