The effects of microorganisms on plant-insect interactions have usually been underestimated. While plant growth-promoting rhizobacteria (PGPR) are known to induce plant defenses, endosymbiotic bacteria hosted by herbivorous insects are often beneficial to the host. Here, we aimed to assess whether PGPR-induced defenses in broad bean plants impact the pea aphid, depending on its genotype and the presence of endosymbionts. We estimated aphid reproduction, quantified defense- and growth-related phytohormones by GC-MS, and measured different plant growth and physiology parameters, after PGPR treatment. In addition, we recorded the feeding behavior of aphids by electropenetrography. We found that the PGPR treatment of broad bean plants reduced the reproduction of one of the pea aphid clones. We highlighted a phenomenon of PGPR-induced plant defense priming, but no noticeable plant growth promotion. The main changes in aphid probing behavior were related to salivation events into phloem sieve elements. We suggest that the endosymbiont Hamiltonella defensa played a key role in plant-insect interactions, possibly helping aphids to counteract plant-induced resistance and allowing them to develop normally on PGPR-treated plants. Our results imply that plant- and aphid-associated microorganisms add greater complexity to the outcomes of aphid-plant interactions.

中文翻译：

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促进植物生长的根瘤菌诱导的系统抗性影响蚜虫的发育和摄食行为。

通常低估了微生物对植物-昆虫相互作用的影响。虽然已知促进植物生长的根际细菌（PGPR）可以诱导植物防御，但草食性昆虫寄主的内共生细菌通常对宿主有益。在这里，我们旨在评估PGPR诱导的蚕豆植物防御是否会影响豌豆蚜虫，具体取决于其基因型和内共生菌的存在。在PGPR处理后，我们通过GC-MS估计了蚜虫的繁殖，定量的防御和生长相关植物激素，并测量了不同的植物生长和生理参数。此外，我们通过电镜记录了蚜虫的摄食行为。我们发现，蚕豆植物的PGPR处理降低了豌豆蚜虫克隆之一的繁殖。我们强调了PGPR诱导的植物防御启动现象，但没有明显的植物生长促进作用。蚜虫探测行为的主要变化与韧皮部筛网元素的流涎事件有关。我们建议内共生哈密​​尔顿菌在植物与昆虫的相互作用中起着关键作用，可能帮助蚜虫抵抗植物诱导的抗性，并使它们在经过PGPR处理的植物上正常发育。我们的结果表明，与植物和蚜虫相关的微生物为蚜虫-植物相互作用的结果增加了更大的复杂性。