A plant-inducible gene of Xanthomonas campestris pv. campestris encodes an exocellular component required for growth in the host and hypersensitivity on nonhosts

Abstract

Using Tn4431, a transposon that allows transcriptional fusions to a promoterless luciferase (lux) operon, we have isolated a nonpathogenic mutant of Xanthomonas campestris pv. campestris, i.e., JS111, that does not incite any of the black rot symptoms on all tested cruciferous host plants (J. J. Shaw, L. G. Settles, and C. I. Kado, Mol. Plant Microbe Interact. 1:3945, 1988). In the study reported here, we determined that in contrast to the wild-type strain, JS111 is unable to induce a hypersensitive necrotic response on nonhost plants such as datura, tomato, and cucumber, suggesting that JS111 is a nonpathogenic, nonhypersensitive Hrp mutant. JS111 displayed culture growth rates, exopolysaccharide production, and protease, pectate lysase, cellulase, amylase, and phosphatase activities comparable to those of the wild-type strain. However, the growth of JS111 in host leaves was markedly attenuated. Coinoculation of JS111 with the wild-type strain in cauliflower or radish leaves rescued the growth deficiency of the mutant to normal levels. The locus mutated in JS11 was cloned and named hrpXc, and transcriptional and genetic complementation analyses of the hrpXc locus were conducted. The regulation of hrpXc expression was also investigated in vitro and in planta, using fusions to a lux or chloramphenicol acetyltransferase reporter gene. The hrpXc gene was found to be strongly induced in radish leaves. This is the first report and analysis of a hrp locus from a Xanthomonas species.In recent years, the application of molecular genetic approaches to plant pathogenic bacteria has led to the identification and isolation of a number of genes involved in the interaction between the bacterium and the plant. These genes can be tentatively classified into four groups relative to the phenotype they confer on the bacteria. (i) hrp (hypersensitive response and pathogenicity) genes are required for pathogenicity on hosts and for the induction of a hypersensitive response (HR) on nonhost plants (1, 2, 23). (ii) dsp (disease-specific) genes are necessary for pathogenicity but do not affect HR induction on nonhosts (6). (iii) avr (avirulence) genes confer race-or cultivar-specific interactions. The avirulence genes are dominant genes and restrict the host range of the bacteria to the cultivars that contain a complementary resistance gene(s) (36, 37). (iv) Of considerable importance are the hsv (host-specific virulence) genes that have been isolated from bacteria with wide host ranges and are required for pathogenicity on only some of the host plants (13, 14, 28; D. Gabriel, ASM News 52:19-25, 1986). hsv genes can extend the host range when introduced in narrow-host-range strains (25,39).In this paper, we report the identification and characterization of a hrp gene from Xanthomonas campestris pv. campestris, the causal agent of the black rot of crucifers, a worldwide and economically important plant disease (40). Hydathodes are the principal natural mode of entry in the plant, although secondary entry sites can develop in the roots ...

Restoration of pathogenicity of avirulent Xanthomonas oryzae pv. oryzae and X. campestris pathovars by reciprocal complementation with the hrpXo and hrpXc genes and identification of HrpX function by sequence analyses

“…To initiate studies of the genes required for pathogenicity, the wellcharacterized hrpXc gene of X. campestns pv. campestris, whose product is essential for pathogenicity in cruciferous plants and for the hypersensitive response on nonhosts (16,17), was used as a probe to isolate a counterpart gene in X. otyzae pv. oryzae.…”

“…This gene is closely related to hrpXc, which is plant inducible and is required for the growth of X. campestris pv. campestris in planta (16). Additional genes required for virulence but not for heterologous hypersensitivity reactions have been cloned from X. campestris pv.…”

A luminescent reporter evidences active expression of Ralstonia solanacearum type III secretion system genes throughout plant infection

“…Studies in various bacterial pathogens have addressed the question of the minimal time necessary for induction of the T3SS genes after contact with the host. In the case of Xanthomonas campestris and Pseudomonas syringae, it has been determined that induction of these genes is strong and rapid (less than 1-2 h after leaf infiltration) (Haapalainen et al, 2011;Kamoun & Kado, 1990;Ortiz-Martín et al, 2010;Thwaites et al, 2004), although their expression over long periods after inoculation has not been addressed. We found that hrpB was transcribed throughout plant infection, and not only at early stages, in contradiction to the current gene regulation model, which predicts a PhcA-dependent repression of hrpB at high bacterial densities Yoshimochi et al, 2009a).…”

Heterologous growth phase- and temperature-dependent expression and H2O2 toxicity protection of a superoxide-inducible monofunctional catalase gene from Xanthomonas oryzae pv. oryzae

“…Plasmid extraction was performed by the alkaline lysis method (31). Xanthomonas genomic DNA was isolated as previously described (21). Cloning experiments were performed as described by Maniatis et al (31).…”

“…Strains of electrocompetent E. coli and Xanthomonas were prepared and electroporated as previously described (21). For Xanthomonas strains, 1 ml of SB medium was added immediately after electroporation and the bacteria were allowed to grow for 4 h before being plated on selective media.…”