The effects of horizontal gene transfer on virulence gene sequences of enterobacterial plant pathogens.

摘要

The purpose of this study was to assess the evolutionary history of the type III secretion virulence determinants among the enterobacterial plant pathogenic genera Erwinia, Brenneria, Pectobacterium, and Pantoea. We used both virulence and housekeeping gene sequences to reconstruct the evolutionary relationships among the plant pathogens, in order to determine whether: (a) virulence gene sequences are congruent to one another, (b) the evolution of virulence genes is congruent to the evolution of housekeeping genes, or if it reflects patterns of horizontal gene transfer, and (c) current hypotheses of the four genera can be reproduced and supported by additional housekeeping genes, also corroborating the core genome hypothesis.;A number of enterobacterial plant and animal pathogens were included in the analyses, and phylogenies were reconstructed based on four virulence hrcC, hrcR, hrcJ, and hrcV, and four housekeeping 165 rDNA, gapA, gyrA, and ompA genes. DNA data matrices were analyzed using maximum likelihood (ML) algorithms, and character support was determined by ML bootstrap and Bayesian analyses. Phylogenetic congruence was evaluated by newly described partition addition bootstrap alteration approach (PABA).;Virulence gene trees of hrcC, hrcR, hrcJ, and hrcV indicate that horizontal gene transfer has indeed played a role in shaping the evolution of virulence and pathogenicity in Erwinia, Brenneria, Pectobacterium, and Pantoea. The trees support a monophyletic origin of the enterobacterial plant pathogens, which is contrary to the housekeeping gene trees of 16S rDNA, gyrA, and ompA, which support a polyphyletic origin of the four genera. Being that lateral transfer is a likely process of auxiliary gene acquisition, Erwinia, Brenneria, Pectobacterium, and Pantoea may have acquired their PAIs independently of one another, and through HGT events, evolution of TTSS has converged to reflect the observed monophyletic origin for the virulence genes of these plant pathogens. In addition, the current taxonomic classification of Erwinia, Brenneria, and Pectobacterium (Hauben et al. 1998), is not supported by either the housekeeping or the virulence gene trees, other than the classification of the genus Pantoea which forms monophyletic group in the 16S rDNA, gapA, and gyrA trees. Consequently, the taxonomic history of the enterobacterial plant pathogens remains undetermined.