Adaptive Evolution Has Targeted the C-Terminal Domain of the RXLR Effectors of Plant Pathogenic Oomycetes
Win. J Morgan. W Bos. J Krasileva. K. V Cano. L. M Chaparro-Garcia. A Ammar. R Staskawicz. B. J Kamoun. S
The Plant Cell ; 2007 [Vol.19] Pages:2349-2369
Abstract
Oomycete plant pathogens deliver effector proteins inside host cells tomodulate plant defense circuitry and toenable parasitic colonization. These effectors are defined by a conservedmotif, termed RXLR (for Arg, any amino acid, Leu, Arg), that is located downstream of the signal peptide and that has been implicated in host translocation. Because the phenotypes of RXLR
effectors extend to plant cells, their genes are expected to be the direct target of the evolutionary forces that drive the antagonistic interplay between pathogen and host. We used the draft genome sequences of three oomycete plant pathogens,Phytophthora sojae, Phytophthora ramorum, and Hyaloperonospora parasitica, to generate genome-wide catalogs of RXLR effector genes and determine the extent to which these genes are under positive selection. These analyses revealed that the RXLR sequence is overrepresented and positionally constrained in the secretome of Phytophthora relative to other eukaryotes. The three examined plant pathogenic oomycetes carry complex and diverse sets of RXLR effector genes that have undergone relatively rapid birth and death evolution.We obtained robust evidence of positive selection inmore than two-thirds of the examined paralog families of RXLR effectors. Positive selection has acted for the most part on the C-terminal region, consistentwith the view that RXLR effectors aremodular, with the N terminus involved in secretion and host translocation and the C-terminal domain dedicated to modulating host defenses inside plant cells.
Full Text