Plant immunity activated and suppressed by a conserved effector protein family in mirid bug Riptortus pedestris

Riptortus pedestris (Fabricius) a major soybean pest migrates into soybean fields during pod filling stage resulting in a leaf and stem staygreen while pods without beans syndrome. Given the agricultural importance of this species and the lack of characterized HAMP from piercing-sucking insects we performed a large scale of screening by expression of 87 R. pedestris salivary proteins with signal peptides in Nicotiana benthamiana obtaining a candidate HAMP RPH1. RPH1 activated a series of PTI responses including ROS burst upregulation of defense marker genes such as PR1 WRKY7 WRKY8 Acre31 and CYP71D20 MAPK activation and biosynthesis of phytohormones in plants. RPH1 significantly enhances soybean resistance against R. pedestris feeding. PRR coreceptors BAK1 and SOBIR1 were required for RPH1-induced PTI responses. Remarkably RPH1 homologs were widely distributed in herbivorous insects and majority of homologs from selected species induced cell death or ROS. Thus our results demonstrated that RPH1 is a conserved HAMP within chewing and piercing-sucking insects. We also discovered that R. pedestris evolved four paralogs to overcome the plant immunity triggered by RPH1. This study filled a major gap of HAMP identification from piercing-sucking insect and also deciphered a novel evasion strategy of plant immunity exploited by herbivorous insects.