Whole-Genome Sequence Analysis of Pseudomonas syringae pv. phaseolicola 1448A Reveals Divergence among Pathovars in Genes Involved in Virulence and Transposition

Abstract

Pseudomonas syringae pv. phaseolicola, a gram-negative bacterial plant pathogen, is the causal agent of halo blight of bean. In this study, we report on the genome sequence of P. syringae pv. phaseolicola isolate 1448A, which encodes 5,353 open reading frames (ORFs) on one circular chromosome (5,928,787 bp) and two plasmids (131,950 bp and 51,711 bp). Comparative analyses with a phylogenetically divergent pathovar, P. syringae pv. tomato DC3000, revealed a strong degree of conservation at the gene and genome levels. In total, 4,133 ORFs were identified as putative orthologs in these two pathovars using a reciprocal best-hit method, with 3,941 ORFs present in conserved, syntenic blocks. Although these two pathovars are highly similar at the physiological level, they have distinct host ranges; 1448A causes disease in beans, and DC3000 is pathogenic on tomato and Arabidopsis. Examination of the complement of ORFs encoding virulence, fitness, and survival factors revealed a substantial, but not complete, overlap between these two pathovars. Another distinguishing feature between the two pathovars is their distinctive sets of transposable elements. With access to a fifth complete pseudomonad genome sequence, we were able to identify 3,567 ORFs that likely comprise the core Pseudomonas genome and 365 ORFs that are P. syringae specific.The gram-negative plant-pathogenic species Pseudomonas syringae is comprised of at least 50 pathovars that can be distinguished by their host ranges (30). Many P. syringae pathovars also contain several races characterized by their avirulence on different host cultivars. Genetic control of host specificity at the race-cultivar level, and possibly the pathovar-host species level, is conditioned by "gene-for-gene" interactions between avirulence genes in the pathogen and the corresponding resistance genes in the plant (35). In the last 2 decades, a number of pathogen avirulence genes, as well as the corresponding host resistance genes, have been cloned and identified (9, 13). Resistance gene products, regardless of whether they encode resistance to viral, bacterial, fungal, nematode, or insect pathogens, share similar structures and with few exceptions contain a leucine-rich repeat region (reviewed in reference 37), suggesting a conserved mechanism(s) for pathogen recognition and signal transduction events. In contrast, avirulence gene products share little sequence similarity, although it is well known that bacterial avirulence gene products, along with other virulence factors collectively termed effectors, are injected into the host cell via the specialized type III secretion system (TTSS) that is conserved among plant and animal pathogens (15). The P. syringae effectors are designated Avr (avirulence) or Hop (Hrp outer protein) according to a recently adopted nomenclature system (38). P. syringae effectors collectively are important to virulence, and increasing evidence suggests that these proteins are involved in suppression of host defense responses in compatible interactions with hos...

Complete genome sequence of the entomopathogenic and metabolically versatile soil bacterium Pseudomonas entomophila

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“…The P. entomophila genome harbors several genes that encode hydrolytic activities such as chitinases, lipases and proteases as well as a set of 19 uncharacterized hydrolases, which are potentially involved in the degradation of polymers found in the soil. However, contrary to phytopathogenic strains such as P. syringae [5][6][7] , the genome of P. entomophila is devoid of genes encoding enzymes capable of degrading plant cell walls. This is consistent with the observation that this species is not pathogenic for plants (M. Arlat, Institut National de la Recherche Agronomique, Castanet, France, personal communication).…”

De novo assembly using low-coverage short read sequence data from the rice pathogen Pseudomonas syringae pv. oryzae

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Genetic analysis of genes involved in dipeptide metabolism and cytotoxicity in Pseudomonas aeruginosa PAO1

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