Comparative Genomic and Phenotypic Characterization of Pathogenic and Non-Pathogenic Strains of Xanthomonas arboricola Reveals Insights into the Infection Process of Bacterial Spot Disease of Stone Fruits.

Jerson Garita-Cambronero,María M López,Ana Palacio-Bielsa,Jaime Cubero,Ulrich Melcher

doi:10.1371/journal.pone.0161977

Abstract

Xanthomonas arboricola pv. pruni is the causal agent of bacterial spot disease of stone fruits, a quarantinable pathogen in several areas worldwide, including the European Union. In order to develop efficient control methods for this disease, it is necessary to improve the understanding of the key determinants associated with host restriction, colonization and the development of pathogenesis. After an initial characterization, by multilocus sequence analysis, of 15 strains of X. arboricola isolated from Prunus, one strain did not group into the pathovar pruni or into other pathovars of this species and therefore it was identified and defined as a X. arboricola pv. pruni look-a-like. This non-pathogenic strain and two typical strains of X. arboricola pv. pruni were selected for a whole genome and phenotype comparative analysis in features associated with the pathogenesis process in Xanthomonas. Comparative analysis among these bacterial strains isolated from Prunus spp. and the inclusion of 15 publicly available genome sequences from other pathogenic and non-pathogenic strains of X. arboricola revealed variations in the phenotype associated with variations in the profiles of TonB-dependent transporters, sensors of the two-component regulatory system, methyl accepting chemotaxis proteins, components of the flagella and the type IV pilus, as well as in the repertoire of cell-wall degrading enzymes and the components of the type III secretion system and related effectors. These variations provide a global overview of those mechanisms that could be associated with the development of bacterial spot disease. Additionally, it pointed out some features that might influence the host specificity and the variable virulence observed in X. arboricola.

Highlights

Xanthomonas arboricola [1] is a species of Gram negative, rod-shaped bacteria exclusively associated with plants
As an initial approach to characterize a group of strains phenotypically similar to Xanthomonas isolated from Prunus in Spain, one Xanthomonas strain isolated from asymptomatic leaves of P. mahaleb, and 14 Xanthomonas strains isolated from Prunus spp. with symptoms of bacterial spot disease, were typed at four loci in order to determine their taxonomic position [18] (Table 1)
We utilized a multilocus sequence analysis (MLSA) scheme proposed by Young and collaborators [18], which is based in the analysis of partial sequences of the genes dnaK, fyuA, gyrB and rpoD

Summary

Introduction

Xanthomonas arboricola [1] is a species of Gram negative, rod-shaped bacteria exclusively associated with plants. Most of the strains of this species cause diseases on several herbaceous and woody plants of agricultural interest. Some other strains have been identified as non-pathogenic, saprophytic or opportunistic pathogens. Based on the host specialization of the pathogenic strains, nine pathovars have been recently proposed [2]. Pruni, causal agent of bacterial spot disease on at least 13 species of the genus Prunus, is considered one of the most economically important pathovars within X. arboricola. This pathogen, which is classified as a quarantinable organism in the European Union, causes damages on leaves, fruits, twigs, branches and trunks of the trees [3]. Damages in 25–75% of the peach fruits in orchards in the USA have been reported [4]

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