Cai, RongmanLewis, JamesYan, ShuangchunClarke, Christopher R.Campanile, FrancescoAlmeida, Nalvo F.Studholme, David J.Lindeberg, MagdalenSchneider, DavidZaccardelli, MassimoSetubal, João C.Morales-Lizcano, Nadia P.Bernal, AdrianaCoaker, GittaBaker, ChristyBender, Carol L.Leman, Scotland C.Vinatzer, Boris A.2014-04-092014-04-092011-08-25Cai R, Lewis J, Yan S, Liu H, Clarke CR, et al. (2011) The Plant Pathogen Pseudomonas syringae pv. tomato Is Genetically Monomorphic and under Strong1553-7374http://hdl.handle.net/10919/47004Recently, 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.en-USCreative Commons CC0 1.0 Universal Public Domain DedicationBacterial genomicsGenome evolutionLeavesPhylogenetic analysisArticle - Refereedhttp://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1002130https://doi.org/10.1371/journal.ppat.1002130