Insights into Genome Plasticity and Pathogenicity of the Plant Pathogenic BacteriumXanthomonas campestrispv. vesicatoria Revealed by the Complete Genome Sequence

Abstract

The gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria is the causative agent of bacterial spot disease in pepper and tomato plants, which leads to economically important yield losses. This pathosystem has become a well-established model for studying bacterial infection strategies. Here, we present the whole-genome sequence of the pepper-pathogenic Xanthomonas campestris pv. vesicatoria strain 85-10, which comprises a 5.17-Mb circular chromosome and four plasmids. The genome has a high G؉C content (64.75%) and signatures of extensive genome plasticity. Whole-genome comparisons revealed a gene order similar to both Xanthomonas axonopodis pv. citri and Xanthomonas campestris pv. campestris and a structure completely different from Xanthomonas oryzae pv. oryzae. A total of 548 coding sequences (12.2%) are unique to X. campestris pv. vesicatoria. In addition to a type III secretion system, which is essential for pathogenicity, the genome of strain 85-10 encodes all other types of protein secretion systems described so far in gramnegative bacteria. Remarkably, one of the putative type IV secretion systems encoded on the largest plasmid is similar to the Icm/Dot systems of the human pathogens Legionella pneumophila and Coxiella burnetii. Comparisons with other completely sequenced plant pathogens predicted six novel type III effector proteins and several other virulence factors, including adhesins, cell wall-degrading enzymes, and extracellular polysaccharides. Xanthomonas campestris pv. vesicatoria (also designatedXanthomonas axonopodis pv. vesicatoria [101] or Xanthomonas euvesicatoria [46]) is a gram-negative, rod-shaped ␥-proteobacterium with a high genomic GϩC content. Members of the genus Xanthomonas represent an omnipresent group of plantpathogenic bacteria which infect most economically important crop plants and cause a broad variety of diseases (54). X. campestris pv. vesicatoria, the causative agent of bacterial spot disease on pepper (Capsicum spp.) and tomato (Lycopersicon spp.) plants, enters the plant tissue through stomata and wounds. Bacterial colonization of plant intercellular spaces is locally restricted and induces macroscopically visible disease symptoms, so-called water-soaked lesions that later become necrotic (91). The disease results in defoliation and severely spotted fruits, both of which cause massive yield losses. Bacterial spot disease occurs worldwide but is most pernicious in regions with a warm and humid climate.Pathogenicity of X. campestris pv. vesicatoria depends on a type III protein secretion system (TTSS) (11, 17), which is highly conserved among plant and animal pathogenic bacteria (24, 97). In X. campestris pv. vesicatoria, the TTSS is encoded by the chromosomal hrp gene cluster (hypersensitive response and pathogenicity) (11) and translocates effector proteins into the plant cell (96). Once inside the plant cytoplasm, the effectors modulate host cell processes, such as suppression of the plant basal defense mechanisms, for the benefit of the pathog...

Complete genome of the mutualistic, N2-fixing grass endophyte Azoarcus sp. strain BH72

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“…In a first step automatic gene prediction and annotation were performed using the genome annotation system GenDB 2.0 (ref. 38) as previously described 14 . In a second step the coding sequences (CDS) prediction was validated: a position weight matrix (PWM) was generated to score all translation starts, and visualization of CDS was done using GeneQuest (DNASTAR Inc.).…”

A Conserved Carboxylesterase Is a SUPPRESSOR OF AVRBST-ELICITED RESISTANCE inArabidopsis

“…Bioinformatics and functional genetic screens have been used to identify and characterize the T3S effector proteome in the genome of Xcv 85-10, a model strain used to study bacterial spot (Roden et al, 2004a;Thieme et al, 2005;Gurlebeck et al, 2006). Although numerous effectors (>30) have been identified (Gurlebeck et al, 2006), the biochemical function of these proteins in promoting bacterial colonization within the host, resulting in either disease or resistance signaling, is poorly understood.…”

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“…The alignment in Figure 1 shows that the cysteine peptidase from Xac is similar to those of other phytopathogenic organisms such as X. vesicatoria (80% similarity), which is the causal agent of bacterial spot disease in tomatoes and peppers (Thieme et al, 2005). This high degree of similarity was expected, as both organisms belong to the family Xanthomonadaceae.…”