Comparative genomics reveals diversity among xanthomonads infecting tomato and pepper

<p>Abstract</p> <p>Background</p> <p>Bacterial spot of tomato and pepper is caused by four <it>Xanthomonas </it>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, <it>Xanthomonas euvesicatoria </it>(<it>Xcv</it>) 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.</p> <p>Results</p> <p>We sequenced the genomes of <it>X. vesicatoria </it>(<it>Xv</it>) strain 1111 (ATCC 35937), <it>X. perforans </it>(<it>Xp</it>) strain 91-118 and <it>X. gardneri </it>(<it>Xg</it>) strain 101 (ATCC 19865). The genomes were compared with each other and with the previously sequenced <it>Xcv </it>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 <it>Xg </it>strain 101 and <it>Xv </it>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 <it>Xcv</it>. 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.</p> <p>Conclusions</p> <p>Comparative 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.</p

Raças de Xanthomonas spp. associadas à mancha-bacteriana em tomate para processamento industrial no Brasil Races of Xanthomonas spp. associated to bacterial spot in processing tomatoes in Brazil

A grande diversidade genética dos agentes causadores da mancha-bacteriana dificulta sobremaneira o desenvolvimento de variedades de pimentão e tomate com resistência durável. Setenta e dois isolados de Xanthomonas spp. provenientes de campos comerciais de tomate para processamento industrial dos estados de Goiás, Minas Gerais, Pernambuco e Bahia foram classificados em raças com base nas reações de genótipos diferenciais de tomateiro (Walter, Hawaii 7998 e NIL 216) e de Capsicum (ECW [Early Calwonder], ECW-10R, ECW-20R, ECW-30R e PI235047). As plantas foram inoculadas no estádio de três a cinco folhas verdadeiras por infiltração de suspensão bacteriana (5 ´ 10(8) UFC/ml) na superfície abaxial da folha. Em seguida, foram mantidas em câmara de crescimento em fotoperíodo de 12 h/12 h (luz/escuro) a 28ºC. A reação de hipersensibilidade foi observada até 36 horas após a inoculação, dependendo do genótipo da hospedeira. Foram identificadas as raças T1P2, T1P8 e T3 em X. axonopodis pv. vesicatoria; a raça T2 em X. vesicatoria; e as raças T2P7 e T2P8 em X. gardneri. A presença dos genes avrRxv e avrXv3 nos isolados que causaram reação de hipersensibilidade em 'Hawaii 7998' (raça T1) e 'NIL 216' (raça T3), respectivamente, foi confirmada por reação em cadeia da polimerase (PCR) usando iniciadores específicos. Este é o primeiro relato da ocorrência no Brasil das raças T3, T1P8, T2P7 e T2P8.<br>The great genetic diversity of the causal agents of bacterial spot is the main problem to the development of tomato and pepper varieties with durable resistance. Seventy two strains of Xanthomonas spp. collected from commercial fields of processing tomatoes in the states of Goiás, Minas Gerais, Pernambuco, and Bahia were classified in races according to their reactions on differential genotypes of tomato (Walter, Hawaii 7998 and NIL 216) and Capsicum [ECW (Early Calwonder), ECW-10R, ECW-20R, ECW-30R and PI 235047]. Bacterial suspensions (5 ´ 10(8) UFC/ml) were infiltrated in the abaxial leaf face of the plants at the three to five true-leaf stage. The plants were then kept in a growth chamber at 28ºC and a 12-h light/dark photoperiod. The response reactions were observed up to 36 hours after inoculation, depending on the genotype. Races T1P2, T1P8 and T3 were identified in X. axonopodis pv. vesicatoria; race T2 in X. vesicatoria; and races T2P7 e T2P8 in 'X. gardneri'. The presence of genes avrRxv and avrXv3 was confirmed by polymerase chain reaction (PCR) with specific primers in strains that produced hypersensitive reaction on 'Hawaii 7998' (races T1) and 'NIL 216' (race T3), respectively. This is the first report of races T3, T1P8, T2P7 and T2P8 in Brazil