Aphids secrete diverse repertoires of salivary effectors into host plant cells to promote infestation by modulating plant defence. The greenbug Schizaphis graminum is an important cereal aphid worldwide. However, the secreted effectors of S. graminum are still uncharacterized. Here, 76 salivary proteins were identified from the watery saliva of S. graminum using transcriptome and proteome analyses. Among them, a putative salivary effector Sg2204 was significantly up-regulated during aphid feeding stages, and transient overexpression of Sg2204 in Nicotiana benthamiana inhibited cell death induced by BAX or INF1. Delivering Sg2204 into wheat via the type III secretion system of Pseudomonas fluorescens EtAnH suppressed pattern-triggered immunity (PTI)-associated callose deposition. The transcript levels of jasmonic acid (JA)- and salicylic acid (SA)-associated defence genes of wheat were significantly down-regulated, and the contents of both JA and SA were also significantly decreased after delivery of Sg2204 into wheat leaves. Additionally, feeding on wheat expressing Sg2204 significantly increased the weight and fecundity of S. graminum and promoted aphid phloem feeding. Sg2204 was efficiently silenced via spray-based application of the nanocarrier-mediated transdermal dsRNA delivery system. Moreover, Sg2204-silenced aphids induced a stronger wheat defence response and resulted in negative impacts on aphid feeding behaviour, survival and fecundity. Silencing of Sg2204 homologues from four aphid species using nanocarrier-delivered dsRNA also significantly reduced aphid performance on host plants. Thus, our study characterized the salivary effector Sg2204 of S. graminum involved in promoting host susceptibility by suppressing wheat defence, which can also be regarded as a promising RNAi target for aphid control.

中文翻译：

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青虫 Schizaphis graminum 中的唾液效应蛋白 Sg2204 抑制小麦防御，对于使蚜虫以寄主植物为食至关重要

蚜虫将多种唾液效应器分泌到宿主植物细胞中，通过调节植物防御来促进侵染。Greenbug Schizaphis graminum是世界范围内重要的谷类蚜虫。然而，S. graminum的分泌效应器仍然没有被表征。在这里，使用转录组和蛋白质组分析从S. graminum的水样唾液中鉴定出 76 种唾液蛋白。其中，假定的唾液效应因子 Sg2204 在蚜虫摄食阶段显着上调，并且本氏烟草中 Sg2204 的瞬时过表达抑制了 BAX 或 INF1 诱导的细胞死亡。通过荧光假单胞菌的 III 型分泌系统将 Sg2204 递送到小麦中EtAnH 抑制模式触发免疫 (PTI) 相关的胼胝质沉积。小麦的茉莉酸（JA）和水杨酸（SA）相关防御基因的转录水平显着下调，并且在将Sg2204递送至小麦叶片后，JA和SA的含量也显着降低。此外，饲喂表达 Sg2204 的小麦显着增加了禾谷镰刀菌的重量和繁殖力，并促进了蚜虫韧皮部的取食。Sg2204通过纳米载体介导的经皮 dsRNA 递送系统的喷雾应用有效地沉默。此外，SG2204- 沉默的蚜虫诱导了更强的小麦防御反应，并对蚜虫的摄食行为、生存和繁殖力产生了负面影响。使用纳米载体传递的 dsRNA沉默四种蚜虫物种的Sg2204同源物也显着降低了寄主植物上的蚜虫性能。因此，我们的研究表征了禾谷镰刀菌的唾液效应因子 Sg2204 ，其通过抑制小麦防御来促进宿主易感性，这也可以被视为蚜虫控制的有希望的 RNAi 靶标。