Ralstonia solancearum causes bacterial wilt disease on diverse plant hosts. R. solanacearum cells enter a host from soil or infested water through the roots, then multiply and spread in the water-transporting xylem vessels. Despite the low nutrient content of xylem sap, R. solanacearum grows extremely well inside the host, using denitrification to respire in this hypoxic environment. R. solanacearum growth in planta also depends on the successful deployment of protein effectors into host cells using a Type III Secretion System (T3SS). The T3SS is absolutely required for R. solanacearum virulence, but it is metabolically costly and can trigger host defenses. Thus, the pathogens success depends on optimized regulation of the T3SS. We found that a byproduct of denitrification, the toxic free-radical nitric oxide (NO), positively regulates the R. solanacearum T3SS both in vitro and in planta. Using chemical treatments and R. solanacearum mutants with altered NO levels, we show that the expression of a key T3SS regulator is induced by NO in culture. Analyzing the transcriptome of R. solanacearum responding to varying levels of NO both in culture and in planta revealed that the T3SS and effectors were broadly upregulated with increasing levels of NO. This regulation was specific to the T3SS and was not shared by other stressors. Our results suggest that R. solanacearum experiences an NO-rich environment in the plant host and may use this NO as a signal to activate T3SS during infection.

中文翻译：

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一氧化氮调节Ralstonia solanacearum 3型分泌系统。

雷氏梭菌在多种植物宿主上引起细菌性枯萎病。青枯菌细胞从土壤或受感染的水通过根部进入宿主，然后在输水木质部血管中繁殖并传播。尽管木质部汁液的营养成分较低，但茄形红斑狼疮在宿主体内生长良好，在此低氧环境中使用反硝化作用呼吸。青枯菌在植物中的生长还取决于使用III型分泌系统（T3SS）将蛋白质效应子成功部署到宿主细胞中。T3SS是青枯雷尔氏菌毒力绝对必需的，但是它的代谢成本很高，并且可以触发宿主防御。因此，病原体的成功取决于对T3SS的优化调控。我们发现反硝化的副产物，有毒的自由基一氧化氮（NO），正调节R。茄属植物T3SS在体外和在植物中。使用化学疗法和青枯菌突变的NO水平，我们表明关键的T3SS调节剂的表达是由文化中的NO诱导的。分析青枯菌在培养物中和植物中对不同水平的NO响应的转录组显示，随着NO水平的升高，T3SS和效应子被广泛上调。此规则特定于T3SS，其他压力源未共享该规则。我们的结果表明青枯菌在植物宿主中会遇到一个富含NO的环境，并且可能会将此NO用作感染期间激活T3SS的信号。分析青枯菌在培养物中和植物中对不同水平的NO响应的转录组显示，随着NO水平的升高，T3SS和效应子被广泛上调。此规则特定于T3SS，其他压力源未共享该规则。我们的结果表明青枯菌在植物宿主中会遇到一个富含NO的环境，并且可能会将此NO用作感染期间激活T3SS的信号。分析青枯菌在培养物中和植物中对不同水平的NO响应的转录组显示，随着NO水平的升高，T3SS和效应子被广泛上调。此规则特定于T3SS，其他压力源未共享该规则。我们的结果表明青枯菌在植物宿主中会遇到一个富含NO的环境，并且可能会将此NO用作感染期间激活T3SS的信号。