Comparative genomics reveals diversity among xanthomonads infecting tomato and pepper

Abstract

BackgroundBacterial spot of tomato and pepper is caused by four Xanthomonas species and is a major plant disease in warm humid climates. The four species are distinct from each other based on physiological and molecular characteristics. The genome sequence of strain 85-10, a member of one of the species, Xanthomonas euvesicatoria (Xcv) has been previously reported. To determine the relationship of the four species at the genome level and to investigate the molecular basis of their virulence and differing host ranges, draft genomic sequences of members of the other three species were determined and compared to strain 85-10.ResultsWe sequenced the genomes of X. vesicatoria (Xv) strain 1111 (ATCC 35937), X. perforans (Xp) strain 91-118 and X. gardneri (Xg) strain 101 (ATCC 19865). The genomes were compared with each other and with the previously sequenced Xcv strain 85-10. In addition, the molecular features were predicted that may be required for pathogenicity including the type III secretion apparatus, type III effectors, other secretion systems, quorum sensing systems, adhesins, extracellular polysaccharide, and lipopolysaccharide determinants. Several novel type III effectors from Xg strain 101 and Xv strain 1111 genomes were computationally identified and their translocation was validated using a reporter gene assay. A homolog to Ax21, the elicitor of XA21-mediated resistance in rice, and a functional Ax21 sulfation system were identified in Xcv. Genes encoding proteins with functions mediated by type II and type IV secretion systems have also been compared, including enzymes involved in cell wall deconstruction, as contributors to pathogenicity.ConclusionsComparative genomic analyses revealed considerable diversity among bacterial spot pathogens, providing new insights into differences and similarities that may explain the diverse nature of these strains. Genes specific to pepper pathogens, such as the O-antigen of the lipopolysaccharide cluster, and genes unique to individual strains, such as novel type III effectors and bacteriocin genes, have been identified providing new clues for our understanding of pathogen virulence, aggressiveness, and host preference. These analyses will aid in efforts towards breeding for broad and durable resistance in economically important tomato and pepper cultivars.

Pseudomonas syringae type III effector HopAF1 suppresses plant immunity by targeting methionine recycling to block ethylene induction

“…There also are HopAF1 orthologs in other plant pathogens, such as AvrXv3 from Xanthomonas campestris pv. euvesicatoria (36,37), Ralstonia solanacearum, and Pseudomonas savastoni and Aave_1373 from Acidovorax citrulli (38). The presence of HopAF1 in multiple strains of P. syringae and other plant pathogens suggests it plays an important role in virulence.…”

Comparative Genomic Analysis of Xanthomonas axonopodis pv. citrumelo F1, Which Causes Citrus Bacterial Spot Disease, and Related Strains Provides Insights into Virulence and Host Specificit

“…XopAI is putative effector protein reported only in the three canker-causing strains X. axonopodis pv. citri 306, X. aurantifolii strain B, and X. aurantifolii strain C as well as in one X. vesicatoria strain, namely, 1111 (68,80). The role of XopAI in the virulence of Xanthomonas remains to be characterized.…”

“…X. axonopodis pv. citrumelo consists of a xopC2 gene with its closest homolog in X. perforans, which causes bacterial spot only on tomato (80). X. axonopodis pv.…”

Phytobacterial Type VI Secretion System - Gene Distribution, Phylogeny, Structure and Biological Functions

“…T6SS locus is almost collinear for the T6SS related genes and for the two T6SS-unrelated putative ORF insertions with the T6SS of X.c.v. Whole genome comparisons (Potnis et al, 2011) recently enabled an extensive analysis of the presence and distribution of T6SS among Xanthomonas strains representing 15 pathovars. X.o.…”