Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America.
PLoS Pathog. 2011 Aug;7(8):e1002130. doi: 10.1371/journal.ppat.1002130. Epub 2011 Aug 25.
Recently, genome sequencing of many isolates of genetically monomorphic bacterial human pathogens has given new insights into pathogen microevolution and phylogeography. Here, we report a genome-based micro-evolutionary study of a bacterial plant pathogen, Pseudomonas syringae pv. tomato. Only 267 mutations were identified between five sequenced isolates in 3,543,009 nt of analyzed genome sequence, which suggests a recent evolutionary origin of this pathogen. Further analysis with genome-derived markers of 89 world-wide isolates showed that several genotypes exist in North America and in Europe indicating frequent pathogen movement between these world regions. Genome-derived markers and molecular analyses of key pathogen loci important for virulence and motility both suggest ongoing adaptation to the tomato host. A mutational hotspot was found in the type III-secreted effector gene hopM1. These mutations abolish the cell death triggering activity of the full-length protein indicating strong selection for loss of function of this effector, which was previously considered a virulence factor. Two non-synonymous mutations in the flagellin-encoding gene fliC allowed identifying a new microbe associated molecular pattern (MAMP) in a region distinct from the known MAMP flg22. Interestingly, the ancestral allele of this MAMP induces a stronger tomato immune response than the derived alleles. The ancestral allele has largely disappeared from today's Pto populations suggesting that flagellin-triggered immunity limits pathogen fitness even in highly virulent pathogens. An additional non-synonymous mutation was identified in flg22 in South American isolates. Therefore, MAMPs are more variable than expected differing even between otherwise almost identical isolates of the same pathogen strain.
最近，对遗传单态性细菌人类病原体的许多分离株进行基因组测序，使人们对病原体的微观进化和系统地理学有了新的认识。在这里，我们报告了对细菌植物病原体丁香假单胞菌 pv.番茄的基于基因组的微观进化研究。在分析的基因组序列 3,543,009nt 中，在 5 个测序分离株之间仅鉴定出 267 个突变，这表明该病原体具有近期的进化起源。用 89 个来自世界各地的分离株的基于基因组的标记进行的进一步分析表明，在北美和欧洲存在几种基因型，表明该病原体在这些世界区域之间频繁传播。对与毒力和运动性相关的关键病原体基因座的基于基因组的标记和分子分析均表明正在对番茄宿主进行持续适应。在 III 型分泌效应基因 hopM1 中发现了一个突变热点。这些突变消除了全长蛋白触发细胞死亡的活性，表明该效应子的功能丧失受到强烈选择，而先前该效应子被认为是毒力因子。鞭毛蛋白编码基因 fliC 中的两个非同义突变允许在不同于已知 MAMP flg22 的区域鉴定新的微生物相关分子模式 (MAMP)。有趣的是，该 MAMP 的祖先等位基因比衍生等位基因诱导更强的番茄免疫反应。该祖先等位基因在当今的 Pto 群体中已基本消失，这表明鞭毛蛋白触发的免疫甚至在高度毒力的病原体中也限制了病原体的适应性。在南美分离株中还鉴定到 flg22 中的另一个非同义突变。因此，MAMPs 的变异性比预期的要大，即使在同一病原体菌株的几乎相同的分离株之间也存在差异。
