Evaluation of the Virulence of Xanthomonas campestris pv. campestris Mutant Strains Lacking Functional Genes in the OxyR Regulon

Abstract

Xanthomonas campestris pv. campestris causes black rot in cruciferous crops. Hydrogen peroxide (H(2)O(2)) production and accumulation is an important initial response in plant defense against invading microbes. The role of genes involved in the bacterial H(2)O(2) protection system in pathogenicity was evaluated. Mutants of katA (encoding a monofunctional catalase) and, to a lesser extent, katG (encoding a catalase-peroxidase) and oxyR (encoding a H(2)O(2) sensor and a transcription regulator), are hypersensitive to H(2)O(2) treatments that mimic the plant H(2)O(2) burst. These data correlate with the results of pathogenicity testing that show katA, katG, and oxyR mutants are avirulent on a compatible plant. Moreover, exposure to H(2)O(2) (1, 2, and 4 mM) highly induces the expression of genes in the OxyR regulon, including katA, katG, and ahpC. The avirulent phenotype of the oxyR mutant is partly because of its inability to mount an adaptive response upon exposure to an H(2)O(2) burst. Our data provide insights into important roles of a transcription regulator and other genes involved in peroxide stress protection in the virulence of X. campestris pv. campestris.

Copper chloride induces antioxidant gene expression but reduces ability to mediate H2O2 toxicity in Xanthomonas campestris

“…The exponential-phase cultures were challenged with 75 mM CuCl 2 for 15 min. Total RNA preparation and qRT-PCR were performed as previously described (Buranajitpakorn et al, 2011). Real-time PCR was executed using 20 ng cDNA, SYBR green PCR Master Mix (Applied Biosystems) and a specific primer pair for each gene.…”

“…X. campestris pv. campestris ATCC 33913 (Xcc) wild-type and mutant strains were grown aerobically at 28 uC in Silva-Buddenhagen (SB) medium (Charoenlap et al, 2011) and plant-like medium XVM2 (Wengelnik & Bonas, 1996) as indicated. Exponential-phase cells (OD 600 of 0.5) were used in all experiments.…”

“…Ohr (organic hydroperoxide reductase), whose expression is controlled by OhrR, is upregulated in cells challenged with ROOH and sodium hypochlorite (Chi et al, 2011;Panmanee et al, 2006). Some of these genes, including katA, katG, oxyR and soxR, are required for full virulence of this phytopathogen (Charoenlap et al, 2011;Jittawuttipoka et al, 2009;Mahavihakanont et al, 2012). OxyR and OhrR are thiolbased redox sensors and transcriptional regulators; peroxide activation of OxyR and deactivation of OhrR occur via the oxidation of a thiol group of the sensing cysteine residue and subsequent disulfide bond formation.…”

“…Hence, CuCl 2 treatment enhanced transcription of katA while concomitantly decreasing catalase enzymic activity. As KatA is the principal catalase produced during exponential growth in Xcc (Charoenlap et al, 2011), we tested the effects of copper pretreatment on catalase activity in the Xcc wild-type strain harbouring pKatA plasmid for high expression of katA. Treating bacterial cultures with 75 mM An additional experiment was performed to test whether the CuCl 2 -treated cells reduced catalase activity and high expression of katA was due to post-transcriptional modification of KatA, instability of KatA or other modifications of enzyme activity.…”

Novel Roles of SoxR, a Transcriptional Regulator from X anthomonas campestris, in Sensing Redox-Cycling Drugs and Regulating a Protective Gene That Have Overall Implications for Bacterial Stress Physiology and Virulence on a Host Plant

“…campestris in a susceptible host plant was evaluated. The soxR mutant, the isogenic wild-type strain, and the soxR mutant harboring plasmid pSoxR (soxR/pSoxR) were inoculated into Chinese radish (Raphanus sativus) leaves using a leaf-clipping method described previously (4). The length of the black rot lesion was measured at 14 days postinoculation.…”