The gut microbiome of the cabbage looper is modulated by tomato specialized metabolites. The gut microbiome of the cabbage looper is modulated by tomato specialized metabolites

Plants protect their tissues from insect herbivory with specialized structures and chemicals, such as cuticles, trichomes and specialized metabolites. Bacteria inside the insect gut are also exposed to plant defences and could potentially modify the outcome of plant-insect interactions. To disentangle this complex multi-organism system, we used tomato mutants impaired in the production of specialized metabolites (odorless-2 and jasmonic acid–insensitive1) and two cultivars (Ailsa Craig and Castlemart), exposed them to herbivory by the cabbage looper (Trichoplusia ni) and collected the insect frass for bacterial community analysis. From the plant perspective, epicuticular wax and terpene profiles showed significant differences. In contrast, the total leaf fatty acid composition did not differ among genotypes. From the insect side, larval weight was confirmed/supported the negative association between specialized metabolites and insect performance. Moreover, frass fatty acid profiles were found to be different from the consumed plant material. Lastly, the leaf and insect-gut bacterial communities were compared. The analysis showed that a small fraction of bacterial taxa was shared between leaf and frass samples. Moreover, insect bacterial community abundance and diversity substantially varied relative to plant host genotype. Altogether, these results indicate that plant defensive metabolites can modulate insect-associated bacterial community composition.

植物通过特化结构与化学物质保护自身组织免受昆虫取食为害，例如角质层（cuticle）、腺毛（trichome）以及特化代谢物（specialized metabolites）。昆虫肠道内的细菌同样会暴露于植物防御机制之下，并有潜力改变植物-昆虫互作的结局。为解析这一复杂的多生物体系，我们选取了特化代谢物合成受损的番茄突变体（无气味2（odorless-2）与茉莉酸不敏感1（jasmonic acid–insensitive1））以及两个番茄栽培品种（艾尔莎·克雷格（Ailsa Craig）与卡斯尔马特（Castlemart）），采用甘蓝尺蠖（cabbage looper，学名Trichoplusia ni）对供试材料进行取食处理，并收集昆虫虫粪（frass）用于细菌群落分析。从植物层面分析，表皮蜡质（epicuticular wax）与萜类化合物（terpene）谱存在显著差异；与之相反，不同基因型番茄叶片的总脂肪酸组成并无显著差异。从昆虫层面来看，幼虫体重数据验证了特化代谢物与昆虫生长表现之间的负相关关联。此外，研究发现虫粪的脂肪酸谱与被取食的植物组织存在显著差异。最后，我们对叶片与昆虫肠道的细菌群落进行了比较分析，结果显示叶片样本与虫粪样本仅共享少量细菌分类群（taxa）；同时昆虫细菌群落的丰度与多样性随宿主植物基因型的不同发生显著变化。综上，本研究结果表明，植物防御性代谢物可调控昆虫相关细菌群落的组成结构。