Cai Rongman in his PhD dissertation hypothesized that highly virulent P. syringae crop pathogens with narrow host range might have evolved after the advent of agriculture from ancestral P. syringae strains with wide host range that were adapted to mixed plant communities. I know that P. s. pv. syringae (phylogroup 2) has the smallest number of T3SS effectors and IS in their genome. According to early works (like "Phylogeny of the genus Pseudomonas:intrageneric structure reconstructed from the nucleotide sequences of gyrB and rpoD genes" Microbiology (2000), 146, 2385–2394) Ps pv. syringae is more close to the last common ancestor than other phylogroups, but more recent trees place other groups with more specialized pathovars close to LCA. Can it be that NJ trees are not correct method to obtain true phylogeny of P. syringae?
Hi Alex,
I generally agree with Rongman hypothesis of a specialization of pathovars under environmental selective pressure. But also Cindy's theory of horizontal gene transfer from environmental strains is very fascinating. Most probably the truth lies somewhere in between.
About NJ trees, obviously their phylogenetic strength depends on the genes on which they are builded. Even if MLST analysis of (a bunch of) core genome genes is widely accepted as reliable phylogenetic approach for Pseudomonas syringae, I think that these only cannot be exhaustive. It would be great to compare whole genomes of many strains.... Or at least to analyse several components of the genetic inheritance, possibly having different evolution speeds.
...definitely not an easy question to answer indeed!
Best
Angelo
Anyone doing DNA sequencing on the Pseudomonas strains that create our rain clouds?
@All, thank you for your ideas! I have met the problem analyzing Ps strains by both list of genes used by Berge et al., (2014) (6 genes) and Hwang et al. (2005) (4 genes): NJ (and ME, ML) trees differed of Maximum Parsimony trees, and as I said the last variant was more reasonable from the discussed point of view.
@Craig, Some information about environmental Pss strains was reported by Monteil CL, Cai R, Liu H, Mechan Llontop ME, Leman S, et al. (2013) Nonagricultural reservoirs contribute to emergence and evolution of Pseudomonas syringae crop pathogens. New Phytol 199: 800–811. doi: 10.1111/nph.12316
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