Proteome analysis of the plant-pathogenic bacterium Xanthomonas oryzae pv. oryzae

Mining and characterization of oxidative stress-related binding proteins of parthenolide in Xanthomonas oryzae pv. oryzae

BACKGROUND

Lack of control agents and development of bacterial resistance are emergent problems in the chemical control of rice bacterial blight, therefore novel bactericides against Xanthomonas oryzae pv. oryzae (Xoo, the causal agent of rice bacterial blight) are urgently needed. We previously found that parthenolide (PTL) is a potential lead against Xoo, and PTL inhibits Xoo growth via oxidative stress. However, the mechanism of action of PTL against Xoo needs further elucidation.

RESULTS

In this study, a biotinylated PTL probe was synthesized, and two important subunits in the respiratory chain (NuoF of complex I and SdhB of complex II) of Xoo were captured with the probe and identified with liquid chromatography tandem mass spectrometry (LC-MS/MS). The binding between them was verified with pull-down and drug affinity responsive target stability technologies. In addition, purified proteins of NuoF and SdhB greatly lowered the antibacterial activity of PTL, and PTL evidently inhibited the enzyme activities of complexes I and II. Moreover, knockout of nuoF and sdhB in Xoo caused elevated reactive oxygen species (ROS) levels and increased sensitivity to PTL. Furthermore, molecular simulations indicated that PTL may form covalent bonds with Cys105 and Cys187 in NuoF and Cys106 in SdhB.

CONCLUSION

PTL can directly bind to NuoF and SdhB, which impairs the enzyme functions of complexes I and II in the respiratory chain, leading to ROS accumulation in Xoo. This study will provide deep insight into the mechanism of action of PTL against Xoo. © 2022 Society of Chemical Industry.

Reciprocal adaptation of rice and Xanthomonas oryzae pv. oryzae: cross-species 2D GWAS reveals the underlying genetics

A 1D/2D genome-wide association study strategy was adopted to investigate the genetic systems underlying the reciprocal adaptation of rice (Oryza sativa) and its bacterial pathogen, Xanthomonas oryzae pv. oryzae (Xoo) using the whole-genome sequencing and large-scale phenotyping data of 701 rice accessions and 23 diverse Xoo strains. Forty-seven Xoo virulence-related genes and 318 rice quantitative resistance genes (QR-genes) mainly located in 41 genomic regions, and genome-wide interactions between the detected virulence-related genes and QR genes were identified, including well-known resistance genes/virulence genes plus many previously uncharacterized ones. The relationship between rice and Xoo was characterized by strong differentiation among Xoo races corresponding to the subspecific differentiation of rice, by strong shifts toward increased resistance/virulence of rice/Xoo populations and by rich genetic diversity at the detected rice QR-genes and Xoo virulence genes, and by genome-wide interactions between many rice QR-genes and Xoo virulence genes in a multiple-to-multiple manner, presumably resulting either from direct protein-protein interactions or from genetic epistasis. The observed complex genetic interaction system between rice and Xoo likely exists in other crop-pathogen systems that would maintain high levels of diversity at their QR-loci/virulence-loci, resulting in dynamic coevolutionary consequences during their reciprocal adaptation.

Design, Synthesis, Crystal Structure, and Antimicrobial Evaluation of 6-Fluoroquinazolinylpiperidinyl-Containing 1,2,4-Triazole Mannich Base Derivatives against Phytopathogenic Bacteria and Fungi

A total of 20 1,2,4-triazole Mannich base derivatives bearing the 6-fluoroquinazolinylpiperidinyl moiety were designed, synthesized, and evaluated as antimicrobial agents against phytopathogenic bacteria and fungi according to the molecular hybridization strategy. Of note, the structure of target compound 4h was clearly confirmed through single-crystal X-ray diffraction analysis. The turbidimetric assays indicated that some compounds exhibited excellent antibacterial efficacies in vitro against Xanthomonas oryzae pv. oryzae (Xoo). For example, compounds 4c, 4f, 4j, and 7j had EC₅₀ values of 23.6, 18.8, 23.4, and 24.3 μg/mL, respectively, which were far superior to that of agrobactericide bismerthiazol (EC₅₀ = 92.4 μg/mL). In particular, compound 4f demonstrated a potent anti-Xoo activity approximately five times more active than that of bismerthiazol. Moreover, in vivo assays showed the excellent protective and curative activities of compound 4f against rice bacterial blight, having the potential as an alternative bactericide for controlling Xoo. The structure-activity relationship analysis showed a good pesticide-likeness concerning compound 4f, following Tice's criteria. The anti-Xoo mechanism of compound 4f was preliminarily explored by scanning electron microscopy measurements in living bacteria. Finally, several compounds also exhibited good antifungal activities in vitro against Gibberella zeae at 50 μg/mL. In short, the presented work showed the potential of 6-fluoroquinazolinylpiperidinyl-containing 1,2,4-triazole Mannich base derivatives as effective bactericides for controlling Xoo.

Growth inhibition and metabolomic analysis of Xanthomonas oryzae pv. oryzae treated with resveratrol

Background

Xanthomonas oryzae pv. oryzae (Xoo) can cause destructive bacterial blight in rice. As an antibacterial, resveratrol may inhibit Xoo growth. This study focused on the potential structural-activity relationship of resveratrol and its derivatives against Xoo growth, and ¹H-NMR-based metabolomic analysis was applied to investigate the global metabolite changes in Xoo after resveratrol treatment.

Results

Resveratrol showed the strongest inhibitory effects on Xoo growth compared with its derivatives, which lacked double bonds (compounds 4–6) or hydroxyls were substituted with methoxyls (compounds 7–9). The IC₅₀ of resveratrol against Xoo growth was 11.67 ± 0.58 μg/mL. Results indicated that the double bond of resveratrol contributed to its inhibitory effects on Xoo growth, and hydroxyls were vital for this inhibition. Interestingly, resveratrol also significantly inhibited Xoo flagellum growth. Based on ¹H-NMR global metabolic analysis, a total of 30 Xoo metabolites were identified, the changes in the metabolic profile indicated that resveratrol could cause oxidative stress as well as disturb energy, purine, amino acid, and NAD⁺ metabolism in Xoo, resulting in the observed inhibitory effects on growth.

Conclusions

This study showed that the double bond of resveratrol contributed to its inhibitory effects on Xoo growth, and hydroxyls were also the important active groups. Resveratrol could cause oxidative stress of Xoo cells, and disturb the metabolism of energy, purine, amino acid and NAD +, thus inhibit Xoo growth.

Effects of camptothecin on the rice blast fungus Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae B. Couch is one of the most devastating diseases on rice. Camptothecin (CPT), which was primarily isolated from Camptotheca acuminata, is well-known for its anti-tumor activities, and is also developed as a potential biological pesticide. We previously investigated the anti-microbial activities of CPT against 11 fungi, 3 oomycetes, and 4 bacteria, and found that CPT was strongly effective against M. oryzae, indicating its potential as a lead for developing fungicide against rice blast. However, the anti-fungal effects of CPT on M. oryzae need further elucidation. In this study, the anti-fungal activities of CPT against M. oryzae were further investigated, which revealed that CPT was effective against M. oryzae both in vitro and in vivo. The transcriptome of M. oryzae was analyzed after CPT treatment, which showed that CPT had a strong inhibitory effect on 'translation' and 'carbohydrate metabolism/energy metabolism' of M. oryzae. Some physiology characteristics of M. oryzae were also assayed, which confirmed that CPT inhibited RNA synthesis, protein synthesis, and carbohydrate metabolism/energy metabolism of M. oryzae, and caused membrane damage. The molecular simulation result showed that CPT binds to the interface of DNA-topoisomerase I complex of M. oryzae. In conclusion, CPT is a promising lead for developing fungicide against rice blast. CPT may bind to DNA-topoisomerase I complex of M. oryzae, thus affecting 'translation' and 'carbohydrate metabolism/energy metabolism', leading to cell death.

Crucial role of oxidative stress in bactericidal effect of parthenolide against Xanthomonas oryzae pv. oryzae

BACKGROUND

Xanthomonas oryzae pv. oryzae (Xoo) causes rice bacterial blight, which is one of the most devastating diseases on rice. Parthenolide (PTL) is a sesquiterpene lactone possessing multiple bioactivities. In the preliminary study, we found PTL can totally inhibit the growth of Xoo at 10 mg L^-1 in vitro. In this study, we aim to further evaluate the anti-bacterial activity of PTL against Xoo and discern the role of oxidative stress in its bactericidal effect.

RESULTS

PTL was effective against Xoo both in vitro and in vivo. PTL induced reactive oxygen species (ROS) accumulation in Xoo, leading to cell death, while exogenous catalase can fully abolish its bactericidal effect. PTL sensitivity of catalase deletion mutants of Xoo increased significantly compared with that of wild-type Xoo strain. In addition, PTL treatment increased glutathione peroxidase activity and decreased glutathione (GSH) reductase activity in Xoo, but had no effect on its catalase and superoxide dismutase activities. Interestingly, PTL dramatically reduced the GSH level in Xoo, resulting in disturbed GSH/GSSG balance. Moreover, PTL rapidly reacted with GSH by a nucleophilic addition reaction.

CONCLUSION

PTL is a promising lead compound for developing bactericide against Xoo. PTL rapidly reacts with GSH, resulting in disturbed GSH/GSSG balance in Xoo, which causes ROS accumulation, leading to cell death. Oxidative stress plays a critical role in the bactericidal effect of PTL against Xoo. © 2018 Society of Chemical Industry.

Unravelling potential virulence factor candidates in Xanthomonas citri. subsp. citri by secretome analysis

Citrus canker is a major disease affecting citrus production in Brazil. It's mainly caused by Xanthomonas citri subsp. citri strain 306 pathotype A (Xac). We analysed the differential expression of proteins secreted by wild type Xac and an asymptomatic mutant for hrpB4 (ΔhrpB4) grown in Nutrient Broth (NB) and a medium mimicking growth conditions in the plant (XAM1). This allowed the identification of 55 secreted proteins, of which 37 were secreted by both strains when cultured in XAM1. In this secreted protein repertoire, the following stand out: Virk, Polyphosphate-selective porin, Cellulase, Endoglucanase, Histone-like protein, Ribosomal proteins, five hypothetical proteins expressed only in the wild type strain, Lytic murein transglycosylase, Lipoprotein, Leucyl-tRNA synthetase, Co-chaperonin, Toluene tolerance, C-type cytochrome biogenesis membrane protein, Aminopeptidase and two hypothetical proteins expressed only in the ΔhrpB4 mutant. Furthermore, Peptidoglycan-associated outer membrane protein, Regulator of pathogenicity factor, Outer membrane proteins, Endopolygalacturonase, Chorismate mutase, Peptidyl-prolyl cis-trans isomerase and seven hypothetical proteins were detected in both strains, suggesting that there was no relationship with the secretion mediated by the type III secretory system, which is not functional in the mutant strain. Also worth mentioning is the Elongation factor Tu (EF-Tu), expressed only the wild type strain, and Type IV pilus assembly protein, Flagellin (FliC) and Flagellar hook-associated protein, identified in the wild-type strain secretome when grown only in NB. Noteworthy, that FliC, EF-Tu are classically characterized as PAMPs (Pathogen-associated molecular patterns), responsible for a PAMP-triggered immunity response. Therefore, our results highlight proteins potentially involved with the virulence. Overall, we conclude that the use of secretome data is a valuable approach that may bring more knowledge of the biology of this important plant pathogen, which ultimately can lead to the establishment of new strategies to combat citrus canker.