Badel J L, Charkowski A O, Deng W L, Collmer A
Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA.
Mol Plant Microbe Interact. 2002 Oct;15(10):1014-24. doi: 10.1094/MPMI.2002.15.10.1014.
The ability of Pseudomonas syringae to grow in planta is thought to be dependent upon the Hrp (type III secretion) system and multiple effector proteins that this system injects into plant cells. ORF5 in the conserved effector locus of the P. syringae pv. tomato DC3000 Hrp pathogenicity island was shown to encode a Hrp-secreted protein and to have a similarly secreted homolog encoded in an effector-rich pathogenicity island located elsewhere in the genome. These putative effector genes were designated hopPtoA1 and hopPtoA2, respectively. DNA gel blot analysis revealed that sequences hybridizing with hopPtoA1 were widespread among P. syringae pathovars, and some strains, like DC3000, appear to have two copies of the gene. uidA transcriptional fusions revealed that expression of hopPtoA1 and hopPtoA2 can be activated by the HrpL alternative sigma factor. hopPtoA1 and hopPtoA1/hopPtoA2 double mutants were not obviously different from wild-type P. syringae pv. tomato DC3000 in their ability to produce symptoms or to increase their total population size in host tomato and Arabidopsis leaves. However, confocal laser-scanning microscopy of GFP (green fluorescent protein)-labeled bacteria in Arabidopsis leaves 2 days after inoculation revealed that the frequency of undeveloped individual colonies was higher in the hopPtoA1 mutant and even higher in the hopPtoA1/hopPtoA2 double mutant. These results suggest that hopPtoA1 and hopPtoA2 contribute redundantly to the formation of P. syringae pv. tomato DC3000 colonies in Arabidopsis leaves.
丁香假单胞菌在植物体内生长的能力被认为取决于Hrp（III型分泌）系统以及该系统注入植物细胞的多种效应蛋白。丁香假单胞菌番茄致病变种DC3000的Hrp致病岛保守效应子位点中的开放阅读框5被证明编码一种Hrp分泌蛋白，并且在基因组其他位置富含效应子的致病岛中编码有一个类似的分泌同源物。这些假定的效应子基因分别被命名为hopPtoA1和hopPtoA2。DNA凝胶印迹分析表明，与hopPtoA1杂交的序列在丁香假单胞菌的不同致病型中广泛存在，一些菌株，如DC3000，似乎有该基因的两个拷贝。uidA转录融合显示hopPtoA1和hopPtoA2的表达可被HrpL替代σ因子激活。hopPtoA1突变体和hopPtoA1/hopPtoA2双突变体在产生症状或在宿主番茄和拟南芥叶片中增加其总群体大小的能力方面与野生型丁香假单胞菌番茄致病变种DC3000没有明显差异。然而，接种后2天对拟南芥叶片中绿色荧光蛋白（GFP）标记细菌的共聚焦激光扫描显微镜观察显示，hopPtoA1突变体中未发育的单个菌落频率较高，而在hopPtoA1/hopPtoA2双突变体中甚至更高。这些结果表明，hopPtoA1和hopPtoA2对丁香假单胞菌番茄致病变种DC3000在拟南芥叶片中形成菌落具有冗余作用。
