Data from: The whitefly-associated facultative symbiont Hamiltonella defensa suppresses induced plant defences in tomato

1. Maternally inherited bacterial symbionts are present in many, if not most, insect species. While there is rapidly accumulating evidence that facultative, heritable symbionts often protect insect hosts from natural enemies, there have been few clear examples where facultative symbionts mediate herbivore–plant interactions. 2. The phloem-feeding whitefly, Bemisia tabaci, is a major agricultural pest that frequently harbours facultative symbionts, including Hamiltonella defensa. While H. defensa and other facultative symbionts have been shown to improve whitefly performance on particular food plants, no direct and specific roles for symbiont-mediated interactions with food plants have been identified. 3. Here, we conducted a series of assays to determine whether infection with H. defensa improved whitefly performance on tomato (Solanum lycopersicum) and whether this benefit was associated with symbiont effects on induced plant defences. Finally, we tested whether impacts on induced defences involved in the modulation of a salivary factor. 4. The downregulation of plant defences was associated with increased whitefly fecundity and survival. Feeding by H. defensa-infected whiteflies suppressed JA and JA-related anti-herbivore-induced defences in tomato relative to uninfected controls. That saliva-only treatments of damaged tomato leaves from H. defensa-infected whiteflies suppressed induced plant defences compared to saliva from uninfected controls, suggesting that elicitors in saliva were responsible. Characterization of the putative salivary factor(s) revealed they are likely small (< 3-kDa) and nonproteinaceous. 5. Interestingly, suppression of defences was not observed in SA-deficient NahG plants, indicating that suppression of JA-regulated defences depends on the SA signalling pathway. This finding reveals an intriguing example of the crosstalk between SA and JA signalling pathways and suggests that infection with facultative symbionts can result in the manipulation of induced plant defences to the benefit of the insect host and heritable symbiont. 6. Our results show that the bacterial symbiont H. defensa mediates whitefly–plant interactions by suppressing induced plant defences in tomato. This finding is among the first showing a direct role for facultative symbionts in mediating plant–herbivore interactions and demonstrates a novel tactic for insect herbivores to circumvent plant defences. Symbiont-mediated suppression of plant defences may enhance the deleterious effects of insect pests feeding on important crops.1. 母系遗传的细菌共生体广泛存在于多数乃至绝大多数昆虫物种中。目前已有越来越多的研究表明，兼性可遗传共生菌常可保护昆虫宿主免受天敌侵害，但有关兼性共生菌介导植食者-植物互作的明确例证却寥寥无几。 2. 取食韧皮部的烟粉虱（Bemisia tabaci）是一类重要农业害虫，其体内常携带包括赫氏菌（Hamiltonella defensa）在内的多种兼性共生菌。尽管已有研究证实，赫氏菌及其他兼性共生菌可在特定寄主植物上提升烟粉虱的适合度，但尚未明确共生菌介导的粉虱-植物互作存在直接且特异的作用机制。 3. 本研究通过一系列实验测定，旨在明确赫氏菌感染是否可提升烟粉虱在番茄（Solanum lycopersicum）上的适合度，以及该益处是否与共生菌对植物诱导防御的调控作用相关。最后，我们进一步验证了其对植物诱导防御的影响是否涉及唾液因子的调控。 4. 植物防御的下调与烟粉虱繁殖力及存活率的提升呈正相关。与未感染的对照组相比，感染赫氏菌的烟粉虱取食可抑制番茄体内的茉莉酸（JA）及JA相关抗植食者诱导防御通路。进一步实验发现，仅用感染赫氏菌的烟粉虱唾液处理受损番茄叶片，即可较对照组唾液更显著地抑制植物诱导防御，表明唾液中的激发子是该效应的关键介质。对推定唾液因子的表征显示，这类因子可能为分子量小于3 kDa的非蛋白类物质。 5. 值得注意的是，在水杨酸（SA）缺失型NahG植株中未观察到防御抑制现象，这表明JA调控的防御通路被抑制依赖于SA信号通路。该发现揭示了SA与JA信号通路间一种有趣的交叉互作模式，并提示兼性共生菌的感染可通过调控植物诱导防御，使昆虫宿主与可遗传共生菌共同获益。 6. 本研究结果表明，细菌共生菌赫氏菌可通过抑制番茄的植物诱导防御，介导烟粉虱与番茄的互作关系。这是目前为数不多的明确证实兼性共生菌可直接介导植食者-植物互作的例证之一，同时也揭示了昆虫植食者规避植物防御的全新策略。共生菌介导的植物防御抑制作用，可能会加重取食重要经济作物的昆虫害虫所带来的危害。