Rohmer Laurence, Guttman David S, Dangl Jeffery L
Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Genetics. 2004 Jul;167(3):1341-60. doi: 10.1534/genetics.103.019638.
Many gram-negative pathogenic bacteria directly translocate effector proteins into eukaryotic host cells via type III delivery systems. Type III effector proteins are determinants of virulence on susceptible plant hosts; they are also the proteins that trigger specific disease resistance in resistant plant hosts. Evolution of type III effectors is dominated by competing forces: the likely requirement for conservation of virulence function, the avoidance of host defenses, and possible adaptation to new hosts. To understand the evolutionary history of type III effectors in Pseudomonas syringae, we searched for homologs to 44 known or candidate P. syringae type III effectors and two effector chaperones. We examined 24 gene families for distribution among bacterial species, amino acid sequence diversity, and features indicative of horizontal transfer. We assessed the role of diversifying and purifying selection in the evolution of these gene families. While some P. syringae type III effectors were acquired recently, others have evolved predominantly by descent. The majority of codons in most of these genes were subjected to purifying selection, suggesting selective pressure to maintain presumed virulence function. However, members of 7 families had domains subject to diversifying selection.
许多革兰氏阴性病原菌通过III型分泌系统将效应蛋白直接转运到真核宿主细胞中。III型效应蛋白是易感植物宿主中毒力的决定因素；它们也是在抗性植物宿主中引发特定抗病性的蛋白。III型效应蛋白的进化受多种竞争力量主导：毒力功能保守的可能需求、躲避宿主防御以及对新宿主的可能适应。为了解丁香假单胞菌中III型效应蛋白的进化历史，我们搜索了44种已知或候选的丁香假单胞菌III型效应蛋白以及两种效应蛋白伴侣的同源物。我们研究了24个基因家族在细菌物种间的分布、氨基酸序列多样性以及水平转移的指示特征。我们评估了多样化选择和纯化选择在这些基因家族进化中的作用。虽然一些丁香假单胞菌III型效应蛋白是最近获得的，但其他一些主要是通过遗传进化而来。这些基因中的大多数密码子都受到纯化选择，这表明存在维持假定毒力功能的选择压力。然而，7个家族的成员具有受到多样化选择的结构域。
