College of Plant Protection, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Nanjing Agricultural University, Nanjing, 210095, China.
Mol Plant Microbe Interact. 2018 Dec;31(12):1244-1256. doi: 10.1094/MPMI-03-18-0074-R. Epub 2018 Oct 17.
OxyR and SoxR are two transcriptional regulators in response to oxidative stress in most bacteria, and SoxR has been reported to be activated by the endogenous redox-cycling compound phenazine in phenazine-producing organisms. However, which transcriptional regulator is activated in pathogens treated with the antibiotic phenazine-1-carboxylic acid (PCA) has not been determined. In this study, we found that PCA treatment activated OxyR rather than SoxR in the phytopathogenic bacteria Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola. We also found that X. oryzae pv. oryzae was much more sensitive to PCA and HO and had a defective antioxidant system (i.e., less of total antioxidant capacity and total catalase activity than X. oryzae pv. oryzicola, although X. oryzae pvs. oryzae and oryzicola are very closely related). Based on KEGG sequences, OxyR differs in 10 amino acids in X. oryzae pv. oryzae versus X. oryzae pv. oryzicola. By exchanging OxyR between X. oryzae pvs. oryzae and oryzicola, we elucidated that OxyR contributed to the differences in antioxidant capacity, total catalase activity, and sensitivity to PCA and HO. We also found that OxyR affected X. oryzae pvs. oryzae and oryzicola growth in a nutrient-poor medium, virulence on host plants (rice), and the hypersensitive response on nonhost plants (Nicotiana benthamiana). Thus, OxyR is a critical regulator that relates to the differences in antioxidative stress between X. oryzae pvs. oryzae and oryzicola and contributes to the differences in survival of them against oxidative stress.
OxyR 和 SoxR 是大多数细菌中应对氧化应激的两种转录调节剂，已报道 SoxR 可被内源性氧化还原循环化合物吩嗪在产生吩嗪的生物体中激活。然而，用抗生素吩嗪-1-羧酸（PCA）处理的病原体中哪种转录调节剂被激活尚未确定。在这项研究中，我们发现在植物病原菌稻黄单胞菌 pv. 稻和稻黄单胞菌 pv. 稻中，PCA 处理激活了 OxyR 而不是 SoxR。我们还发现稻黄单胞菌 pv. 稻对 PCA 和 HO 更为敏感，且抗氧化系统存在缺陷（即总抗氧化能力和总过氧化氢酶活性均低于稻黄单胞菌 pv. 稻，尽管稻黄单胞菌 pv. 稻和稻是非常密切相关的）。基于 KEGG 序列，稻黄单胞菌 pv. 稻中的 OxyR 与稻黄单胞菌 pv. 稻相比在 10 个氨基酸上存在差异。通过在稻黄单胞菌 pv. 稻和稻之间交换 OxyR，我们阐明了 OxyR 导致了抗氧化能力、总过氧化氢酶活性以及对 PCA 和 HO 的敏感性的差异。我们还发现 OxyR 影响稻黄单胞菌 pv. 稻和稻的生长在营养贫瘠的培养基中，对宿主植物（水稻）的毒力和对非宿主植物（烟草原生质体）的过敏反应。因此，OxyR 是一个关键的调节剂，与稻黄单胞菌 pv. 稻和稻之间抗氧化应激的差异有关，并有助于它们在氧化应激下存活的差异。
