Brown planthopper salivary protein SISP stabilizes rice OsSR45 to undermine host resistance to insects

The brown planthoppers (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacidae), is a destructive pest of rice. As a piercing-sucking insect, BPH depends critically on salivary proteins to facilitate its infestation. However, the functions of these salivary proteins remain largely unknown. Using transcriptomic, protein interaction, transgenic, and bioassay approaches, we identified a novel salivary protein and characterized its functional roles in rice defense responses. Here, we report that a key BPH salivary protein, termed SR45-interacting salivary protein (SISP), is secreted into rice plants during feeding and interacts with the rice splicing factor OsSR45. We demonstrated that SISP physically binds to OsSR45 in nuclear speckles, with mutual stabilization between the two proteins. Notably, the RG/RGG motif of SISP plays a key functional role in this interaction. Genetic studies using SISP-overexpressing, OsSR45-overexpressing, and OsSR45-knockout rice lines demonstrated that both proteins negatively regulate rice resistance to BPH by suppressing the phenylalanine biosynthesis pathway. RNA-seq data analysis suggested that the alternative splicing mediated by SISP and OsSR45 may indirectly affect the phenylalanine biosynthesis pathway. Furthermore, SISP was shown to be indispensable for BPH survival. We propose a SISP-mediated infestation model for BPH and provide a potential target for pest control.