The in planta transcriptome of Ralstonia solanacearum: conserved physiological and virulence strategies during bacterial wilt of tomato.
The in planta transcriptome of Ralstonia solanacearum: conserved physiological and virulence strategies during bacterial wilt of tomato.
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作者：
Jacobs JM;Babujee L;Meng F;Milling A;Allen C
植物木质部流体被认为是营养贫乏的环境，但青枯病病原菌青枯菌（Ralstonia solanacearum）很好地适应了它，生长到108至109 CFU/g番茄茎。为了更好地理解青枯菌如何在这种生境中成功，我们分析了两种遗传学上不同的青枯菌菌株的转录组，这两种菌株都使番茄枯萎，菌株UW 551（青枯菌II型）和GMI 1000（青枯菌I型）。在番茄青枯病发病早期，我们在培养物或植物木质部中分析了~6 × 108 CFU/ml的细菌基因表达。尽管存在系统发育差异，但这两种菌株以大致相似的模式表达了它们的3，477个共同的正向同源基因，其中约12%的转录组在植物中与在丰富培养基中显著改变。几个主要的代谢途径在发病过程中高度表达。这些途径包括蔗糖吸收和catalysts，这些途径的组件中的基因编码的ESTABY集群。一个UW 551突变体对抗性和敏感番茄以及马铃薯和流行病学上重要的杂草寄主白英的毒力显着降低。在番茄木质部的定殖过程中，功能性的AMPA有助于病原体的竞争适合度，其中含有~300 µM蔗糖。蔗糖诱导了CITA-A的表达，但在更大程度上是由植物生长诱导的。出乎意料的是，45%的基因直接调节的HrpB，转录激活因子的3型分泌系统（T3 SS），在植物中上调高细胞密度。这一结果修改了基于培养物中细菌行为的调控模型，其中该关键毒力因子在高细胞密度下被抑制。这些基因在萎蔫植物中的活跃转录表明T3 SS在整个疾病周期中具有生物学作用。青枯雷尔氏菌是一种广泛分布的引起植物青枯病的病原菌。它给热带农民造成严重的作物损失，造成重大的经济和人类后果。它也是许多破坏性微生物的模型，这些微生物在营养和氧气含量低的导水植物木质部组织中定居。我们从受感染的番茄植株中提取细菌，并全面鉴定了青枯菌在植物致病过程中表达的生物学功能。这揭示了番茄木质部液中蔗糖的意外存在以及病原体对番茄、马铃薯和常见杂草龙葵的毒力对宿主蔗糖的依赖性。此外，R. solanacearum对植物环境高度响应，在植物中表达的几种代谢和毒力功能与纯培养物完全不同。这些结果加强了研究病原体与宿主相互作用的实用性，并表明选择降低蔗糖水平可以产生抗枯萎病的作物。
Plant xylem fluid is considered a nutrient-poor environment, but the bacterial wilt pathogen Ralstonia solanacearum is well adapted to it, growing to 108 to 109 CFU/g tomato stem. To better understand how R. solanacearum succeeds in this habitat, we analyzed the transcriptomes of two phylogenetically distinct R. solanacearum strains that both wilt tomato, strains UW551 (phylotype II) and GMI1000 (phylotype I). We profiled bacterial gene expression at ~6 × 108 CFU/ml in culture or in plant xylem during early tomato bacterial wilt pathogenesis. Despite phylogenetic differences, these two strains expressed their 3,477 common orthologous genes in generally similar patterns, with about 12% of their transcriptomes significantly altered in planta versus in rich medium. Several primary metabolic pathways were highly expressed during pathogenesis. These pathways included sucrose uptake and catabolism, and components of these pathways were encoded by genes in the scrABY cluster. A UW551 scrA mutant was significantly reduced in virulence on resistant and susceptible tomato as well as on potato and the epidemiologically important weed host Solanum dulcamara. Functional scrA contributed to pathogen competitive fitness during colonization of tomato xylem, which contained ~300 µM sucrose. scrA expression was induced by sucrose, but to a much greater degree by growth in planta. Unexpectedly, 45% of the genes directly regulated by HrpB, the transcriptional activator of the type 3 secretion system (T3SS), were upregulated in planta at high cell densities. This result modifies a regulatory model based on bacterial behavior in culture, where this key virulence factor is repressed at high cell densities. The active transcription of these genes in wilting plants suggests that T3SS has a biological role throughout the disease cycle. Ralstonia solanacearum is a widespread plant pathogen that causes bacterial wilt disease. It inflicts serious crop losses on tropical farmers, with major economic and human consequences. It is also a model for the many destructive microbes that colonize the water-conducting plant xylem tissue, which is low in nutrients and oxygen. We extracted bacteria from infected tomato plants and globally identified the biological functions that R. solanacearum expresses during plant pathogenesis. This revealed the unexpected presence of sucrose in tomato xylem fluid and the pathogen’s dependence on host sucrose for virulence on tomato, potato, and the common weed bittersweet nightshade. Further, R. solanacearum was highly responsive to the plant environment, expressing several metabolic and virulence functions quite differently in the plant than in pure culture. These results reinforce the utility of studying pathogens in interaction with hosts and suggest that selecting for reduced sucrose levels could generate wilt-resistant crops.