Lowe-Power Tiffany M, Jacobs Jonathan M, Ailloud Florent, Fochs Brianna, Prior Philippe, Allen Caitilyn
Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, Wisconsin, USA Department of Plant Pathology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Department of Plant Pathology, University of Wisconsin-Madison, Madison, Wisconsin, USA Institut de Recherche pour le Développement, UMR Interactions Plantes Microorganismes Environnement, Montpellier, France.
mBio. 2016 Jun 21;7(3):e00656-16. doi: 10.1128/mBio.00656-16.
Plants use the signaling molecule salicylic acid (SA) to trigger defenses against diverse pathogens, including the bacterial wilt pathogen Ralstonia solanacearum SA can also inhibit microbial growth. Most sequenced strains of the heterogeneous R. solanacearum species complex can degrade SA via gentisic acid to pyruvate and fumarate. R. solanacearum strain GMI1000 expresses this SA degradation pathway during tomato pathogenesis. Transcriptional analysis revealed that subinhibitory SA levels induced expression of the SA degradation pathway, toxin efflux pumps, and some general stress responses. Interestingly, SA treatment repressed expression of virulence factors, including the type III secretion system, suggesting that this pathogen may suppress virulence functions when stressed. A GMI1000 mutant lacking SA degradation activity was much more susceptible to SA toxicity but retained the wild-type colonization ability and virulence on tomato. This may be because SA is less important than gentisic acid in tomato defense signaling. However, another host, tobacco, responds strongly to SA. To test the hypothesis that SA degradation contributes to virulence on tobacco, we measured the effect of adding this pathway to the tobacco-pathogenic R. solanacearum strain K60, which lacks SA degradation genes. Ectopic addition of the GMI1000 SA degradation locus, including adjacent genes encoding two porins and a LysR-type transcriptional regulator, significantly increased the virulence of strain K60 on tobacco. Together, these results suggest that R. solanacearum degrades plant SA to protect itself from inhibitory levels of this compound and also to enhance its virulence on plant hosts like tobacco that use SA as a defense signal molecule.
Plant pathogens such as the bacterial wilt agent Ralstonia solanacearum threaten food and economic security by causing significant losses for small- and large-scale growers of tomato, tobacco, banana, potato, and ornamentals. Like most plants, these crop hosts use salicylic acid (SA) both indirectly as a signal to activate defenses and directly as an antimicrobial chemical. We found that SA inhibits growth of R. solanacearum and induces a general stress response that includes repression of multiple bacterial wilt virulence factors. The ability to degrade SA reduces the pathogen's sensitivity to SA toxicity and increases its virulence on tobacco.
植物利用信号分子水杨酸（SA）来触发对多种病原体的防御，包括青枯病病原菌茄科雷尔氏菌。SA还能抑制微生物生长。茄科雷尔氏菌复合种的大多数测序菌株可通过龙胆酸将SA降解为丙酮酸和富马酸。茄科雷尔氏菌菌株GMI1000在番茄致病过程中表达这种SA降解途径。转录分析表明，亚抑制水平的SA诱导了SA降解途径、毒素外排泵以及一些一般应激反应的表达。有趣的是，SA处理抑制了包括III型分泌系统在内的毒力因子的表达，这表明这种病原体在受到胁迫时可能会抑制毒力功能。缺乏SA降解活性的GMI1000突变体对SA毒性更敏感，但在番茄上保留了野生型的定殖能力和毒力。这可能是因为SA在番茄防御信号传导中不如龙胆酸重要。然而，另一种寄主烟草对SA反应强烈。为了验证SA降解有助于在烟草上致病的假设，我们测量了将该途径添加到缺乏SA降解基因的烟草致病菌株K60中的效果。异位添加GMI1000的SA降解位点，包括编码两个孔蛋白和一个LysR型转录调节因子的相邻基因，显著增加了菌株K60在烟草上的毒力。总之，这些结果表明，茄科雷尔氏菌降解植物SA以保护自身免受该化合物抑制水平的影响，并增强其在像烟草这样将SA用作防御信号分子的植物寄主上的毒力。
植物病原体如青枯病病原菌茄科雷尔氏菌通过给番茄、烟草、香蕉、马铃薯和观赏植物的小规模和大规模种植者造成重大损失，威胁粮食和经济安全。与大多数植物一样，这些作物寄主间接将水杨酸（SA）用作激活防御的信号，直接用作抗菌化学物质。我们发现SA抑制茄科雷尔氏菌的生长，并诱导包括抑制多种青枯病毒力因子在内的一般应激反应。降解SA的能力降低了病原体对SA毒性的敏感性，并增加了其在烟草上的毒力。
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