Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Latham Hall, Ag Quad Lane, Blacksburg 24061, USA.
Mol Plant Microbe Interact. 2010 Feb;23(2):198-210. doi: 10.1094/MPMI-23-2-0198.
Pseudomonas syringae is best known as a plant pathogen that causes disease by translocating immune-suppressing effector proteins into plant cells through a type III secretion system (T3SS). However, P. syringae strains belonging to a newly described phylogenetic subgroup (group 2c) are missing the canonical P. syringae hrp/hrc cluster coding for a T3SS, flanking effector loci, and any close orthologue of known P. syringae effectors. Nonetheless, P. syringae group 2c strains are common leaf colonizers and grow on some tested plant species to population densities higher than those obtained by other P. syringae strains on nonhost species. Moreover, group 2c strains have genes necessary for the production of phytotoxins, have an ice nucleation gene, and, most interestingly, contain a novel hrp/hrc cluster, which is only distantly related to the canonical P. syringae hrp/hrc cluster. This hrp/hrc cluster appears to encode a functional T3SS although the genes hrpK and hrpS, present in the classical P. syringae hrp/hrc cluster, are missing. The genome sequence of a representative group 2c strain also revealed distant orthologues of the P. syringae effector genes avrE1 and hopM1 and the P. aeruginosa effector genes exoU and exoY. A putative life cycle for group 2c P. syringae is discussed.
丁香假单胞菌是一种众所周知的植物病原体，通过 III 型分泌系统（T3SS）将免疫抑制效应蛋白转运到植物细胞中，从而引起疾病。然而，属于新描述的系统发育亚群（2c 组）的丁香假单胞菌菌株缺少经典的丁香假单胞菌编码 T3SS、侧翼效应子基因座以及任何已知丁香假单胞菌效应子的紧密同源物的 hrc 簇。尽管如此，丁香假单胞菌 2c 组菌株是常见的叶片定殖者，在一些测试的植物物种上生长到比其他非宿主物种上的丁香假单胞菌菌株更高的种群密度。此外，2c 组菌株具有产生植物毒素所需的基因，具有冰核基因，最有趣的是，含有一个新的 hrc 簇，该簇与经典的丁香假单胞菌 hrc 簇仅有远缘关系。尽管经典的丁香假单胞菌 hrc 簇中存在的基因 hrpK 和 hrpS 缺失，但该 hrc 簇似乎编码一个功能性 T3SS。代表 2c 组的菌株的基因组序列还揭示了丁香假单胞菌效应基因 avrE1 和 hopM1 以及铜绿假单胞菌效应基因 exoU 和 exoY 的远缘同源物。讨论了 2c 组丁香假单胞菌的可能生命周期。
