Two thiadiazole compounds promote rice defence against Xanthomonas oryzae pv. oryzae by suppressing the bacterium's production of extracellular polysaccharides

Abstract

Thiazole, isothiazole, thiadiazole, and their derivatives are used to control various human, animal and plant diseases. In addition to having direct anti-microbial and anti-fungal properties, these compounds are thought to induce host defences, but the mechanism of defence induction remains poorly understood. This article reports that the thiadiazoles of zinc thiazole and bismerthiazol induce H2 O2 accumulation, up-regulation of defence-related genes, callose deposition and hypersensitive response-like cell death in rice leaves infected with Xanthomonas oryaze pv. oryzae (Xoo) strain ZJ173, but not in non-infected leaves. These defence responses in Xoo-infected leaves were suppressed by the exogenous application of catalase, which reduces H2 O2 accumulation. The application of extracellular polysaccharides (EPSs) extracted from strain ZJ173 significantly compromised rice defence against ZJ173 with or without thiadiazole treatment. The EPS-deficient Xoo mutant ∆gumH triggered a stronger defence than its parent strain ZJ173. The thiadiazole treatments reduced EPS production by strain ZJ173, but not by the thiadiazole-resistant strain 2-1-1, which is thiadiazole resistant in vivo, but not in vitro; moreover, enhanced defence was not detected in thiadiazole-treated rice inoculated with 2-1-1. Based on these data, we infer that zinc thiazole and bismerthiazol promote rice defence against Xoo by inhibiting the production of bacterial EPS.

A thiadiazole reduces the virulence of Xanthomonas oryzae pv. oryzae by inhibiting the histidine utilization pathway and quorum sensing

“…Interestingly, the expression of all 13 genes was inhibited by bismerthiazol. A previous study has reported that bismerthiazol promotes rice defence by suppressing the bacterium's production of EPS (Liang et al ., ). In the current study, we found that the hut operons did not affect the production of EPS in Xoo (Fig.…”

“…D). A previous study has reported that bismerthiazol does not reduce the EPS production of 2‐1‐1 (Liang et al ., ). We therefore infer that bismerthiazol does not inhibit the QS of 2‐1‐1.…”

“…). AMT, but not ATDA or BTH, also repressed the Hut pathway of Xoo ; this was consistent with a previous study (Liang et al ., , ) and suggests that inhibition by bismerthiazol depends on its sulfhydryl group, which BTH and ATDA lack (Fig. ).…”

“…Genome-wide mRNAs in Xoo were sequenced to monitor the global changes in gene expression of Xoo exposed to 30 mg/L bismerthiazol for 4.5 and 9 h. Here, we did not analyse the control for 9 h by RNA-seq as we have shown previously that the low volume of N,N-dimethylformamide does not affect the physiological and biochemical status of Xoo (Liang et al, 2015(Liang et al, , 2016Zhu et al, 2013). High-throughput RNA-seq generated 9.24-9.74 million single-end reads for each sample.…”

“…EPS production was determined when bacteria had grown to a population density of 2 3 OD and measured as described previously (Liang et al, 2015).…”