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IN BRIEF

Adaptive Evolution among Plant Pathogenic Oomycte RXLR Effector Genes

neckardt{at}aspb.org

Oomycete plant pathogens deliver effector proteins inside host cells, which enable parasitic colonization by modulating plant defense signaling pathways. Effectors are defined by the conserved motif RXLR (Arg, any amino acid, Leu, Arg), which is implicated in delivery of the effector into host cells. Effector proteins have a modular structure, wherein the N-terminal domain contains the signal peptide and RXLR motif that function in secretion and targeting, and the C-terminal region carries the effector activity that acts inside the plant cell. This modular structure suggests that the two domains might be under different selection pressures. Win et al. (pages 2349–2369) 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 three fungi carry highly complex and diverse sets of RXLR effector genes that appear to have undergone rapid evolution. Robust evidence of positive selection, acting mainly on the C-terminal region, was found in over two-thirds of the examined paralog families of RXLR genes. This work provides strong support for the idea that RXLR effectors are modular and that distinct selection pressures have acted on the N-terminal and C-terminal modules.

View larger version (13K): [in this window] [in a new window] [as a PowerPoint slide]   Posterior probabilities from a multiple sequence alignment of five paralogous effector genes from P. ramorum reveal sites under positive selection (shown in red) mainly in the C-terminal effector domain.

www.plantcell.org/cgi/doi/10.1105/tpc.107.190811

Related articles in Plant Cell:

Adaptive Evolution Has Targeted the C-Terminal Domain of the RXLR Effectors of Plant Pathogenic Oomycetes

Joe Win, William Morgan, Jorunn Bos, Ksenia V. Krasileva, Liliana M. Cano, Angela Chaparro-Garcia, Randa Ammar, Brian J. Staskawicz, and Sophien Kamoun
Plant Cell 2007 19: 2349-2369. [Abstract] [Full Text]  

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