Abstract：Aphids secrete diverse repertoires of salivary effectors into host plant cells to promote infestation by modulating plant defense. 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 upregulated 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 defense genes of wheat were significantly downregulated, 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 defense response and resulted in negative impacts on aphid feeding behavior, survival, and fecundity. Silencing of  Sg2204  homologs 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 defense, which can also be regarded as a promising RNAi target for aphid control.

Plant Biotechnology Journal,  IF：13.263

Doi: doi.org/10.1111/pbi.13900