Pseudomonas solanacearum genes controlling both pathogenicity on tomato and hypersensitivity on tobacco are clustered

Abstract

A pLAFR3 cosmid clone designated pVir2 containing a 25-kilobase (kb) DNA insert was isolated from a wild-type Pseudomonas solanacearum GMI1000 genomic library. This cosmid was shown to complement all but one of the nine TnS-induced mutants which have been isolated after random mutagenesis and which have lost both pathogenicity toward tomato and ability to induce hypersensitive reaction (HR) on tobacco (hrp mutants). The insert is colinear with the genome and provides restoration of the HR-inducing ability when transferred into several TnS-induced hrp mutants, but failed to complement deletion mutants extending on both sides of the pVir2 region. Localized mutagenesis demonstrated that the hrp genes are clustered within a 17.5-kb region of pVir2 and that this cluster probably extends on the genomic region adjacent to the pVir2 insert. A 3-kb region adjacent to the hip cluster modulates aggressiveness toward tomato but does not control HR-inducing ability. Sequences within the hip cluster of pVir2 have homology with the genomic DNA of Xanthomonas campestris strains representing eight different pathovars, suggesting that a set of common pathogenicity functions could be shared by P. solanacearum and X. campestris.

Genetic and transcriptional organization of the hrp cluster of Pseudomonas syringae pv. phaseolicola

“…As noted previously by us and other authors (2,5,7,14,24,25,37,39,44,45) (11, 30, 36a). Some hrp genes are expressed in vitro but only under certain conditions (30,47 …”

“…The cluster is located on the chromosome of strain NPS3121. Although we did not examine other strains of the pathogen in this regard, it is interesting to note that an hrp cluster of similar size described in P. solanacearum is located on a megaplasmid (2). This is also the case with other large gene groups that control the plant-bacterium interactions in crown gall disease and in Rhizobium-legume symbiosis.…”

“…Besides P. syringae pv. phaseolicola, hrp genes and/or gene clusters from several other members of the P. syringae taxon have been described and cloned (5, 13-16, 24, 30, 33, 37-39), as have those from phylogenetically distinct plant pathogens, such as Pseudomonas solanacearum (2, 14), Erwinia amylovora (44, 45), and some pathovars of Xanthomonas campestris (2,6,42). Homology between hrp genes has been reported among members of the P. syringae taxon (8a, 24) as well as between P. solanacearum and members of the X. campestris group (2).…”

“…phaseolicola and other phytopathogenic bacteria has been carried out (2,16,24,30,31,36), none of these regions has been fully characterized in respect to its overall genetic organization, such as the number of complementation groups and the transcriptional orientation of the various genes.…”

“…phaseolicola with reporter insertions, (ii) analyze the mutations for their phenotypic effect on the bacterium-host and bacterium-nonhost interactions, (iii) establish the genetic and transcriptional organization of the cluster, and (iv) determine the ability of hrp mutants representing each distinct complementation group to multiply in the leaves of a susceptible host. Since the hrp cluster of P. solanacearum (2), the virulence and tumor-inducing genes of Agrobacterium spp. (32), and the symbiotic gene clusters of Rhizobium spp.…”