Win Joe, Morgan William, Bos Jorunn, Krasileva Ksenia V, Cano Liliana M, Chaparro-Garcia Angela, Ammar Randa, Staskawicz Brian J, Kamoun Sophien
Department of Plant Pathology, Ohio State University Ohio Agricultural Research and Development Center, Wooster, Ohio 44691, USA.
Plant Cell. 2007 Aug;19(8):2349-69. doi: 10.1105/tpc.107.051037. Epub 2007 Aug 3.
Oomycete plant pathogens deliver effector proteins inside host cells to modulate plant defense circuitry and to enable parasitic colonization. These effectors are defined by a conserved motif, 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 in more than two-thirds of the examined paralog families of RXLR effectors. Positive selection has acted for the most part on the C-terminal region, consistent with the view that RXLR effectors are modular, with the N terminus involved in secretion and host translocation and the C-terminal domain dedicated to modulating host defenses inside plant cells.
卵菌植物病原体将效应蛋白输送到宿主细胞内，以调节植物防御机制并实现寄生定殖。这些效应蛋白由一个保守基序定义，称为RXLR（代表精氨酸、任意氨基酸、亮氨酸、精氨酸），该基序位于信号肽下游，与宿主转运有关。由于RXLR效应蛋白的表型延伸到植物细胞，它们的基因有望成为驱动病原体与宿主之间拮抗相互作用的进化力量的直接靶点。我们利用三种卵菌植物病原体——大豆疫霉、栎树疫霉和寄生霜霉的基因组草图序列，生成了RXLR效应蛋白基因的全基因组目录，并确定了这些基因受到正选择的程度。这些分析表明，相对于其他真核生物，RXLR序列在疫霉的分泌组中出现频率过高且位置受限。所研究的三种植物病原卵菌携带复杂多样的RXLR效应蛋白基因集，这些基因经历了相对快速的产生和消亡进化。我们在超过三分之二的所研究的RXLR效应蛋白旁系同源家族中获得了正选择的有力证据。正选择主要作用于C末端区域，这与RXLR效应蛋白是模块化的观点一致，即N末端参与分泌和宿主转运，而C末端结构域专门用于调节植物细胞内的宿主防御。
