Aphids often carry facultative symbionts to achieve diverse advantages. Serratia symbiotica, one of facultative endosymbionts, increases aphid tolerance to heat. However, whether it benefits aphid colonization on host plants is yet to be determined. In the current study, we found that Acyrthosiphon pisum harbouring S. symbiotica had longer feeding duration on Medicago truncatula than Serratia‐free aphids. Contrastingly, Serratia‐free aphids triggered higher accumulation of reactive oxygen species (ROS), jasmonic acid and salicylic acid responsive genes and cytosolic Ca²⁺ elevations than Serratia‐infected aphids. Transcriptomic analysis of salivary glands indicated that a histidine‐rich Ca²⁺‐binding protein‐like gene (ApHRC) was expressed more highly in the salivary gland of Serratia‐infected aphids than that of Serratia‐free aphids. Once ApHRC was silenced, Serratia‐infected aphids also displayed shorter phloem‐feeding duration and caused Ca²⁺ elevation and ROS accumulation in plants. Our results suggest that ApHRC, a potential effector up‐regulated by S. symbiotica in the salivary glands, impairs plant defence response by suppressing Ca²⁺ elevation and ROS accumulation, allowing colonization of aphids. This study has provided an insight into how facultative symbionts facilitate aphid colonization and adaptation to host plants.

中文翻译：

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蚜虫兼性共生体通过操纵唾液腺中的蚜虫基因表达来抑制植物防御。

蚜虫经常携带兼性共生以取得各种优势。共生沙雷氏菌，兼性共生体之一，增加了蚜虫对热的耐受性。但是，是否有利于蚜虫在寄主植物上定植尚待确定。在目前的研究中，我们发现，豌豆蚜窝藏S. symbiotica有更长的喂养时间苜蓿比沙雷-免费蚜虫。与此相反，沙雷-free蚜虫触发活性氧物质的更高的积累（ROS），茉莉酸和水杨酸应答基因和细胞内的Ca ²⁺比隆起沙雷感染的蚜虫。唾液腺的转录组学分析表明，富含组氨酸的Ca ²⁺结合蛋白样基因（ApHRC）在沙雷氏菌感染的蚜虫的唾液腺中的表达高于无沙雷氏菌的蚜虫。一旦将ApHRC沉默，感染沙雷氏菌的蚜虫也表现出较短的韧皮部喂食时间，并导致植物中Ca ²⁺升高和ROS积累。我们的结果表明，唾液共生链球菌上调的潜在效应子ApHRC通过抑制Ca ^2+来损害植物防御反应。升高和ROS积累，使蚜虫定植。该研究提供了关于兼性共生体如何促进蚜虫定植和适应寄主植物的见解。