The Mechanism Of A Salivary Calcium-binding Protein From Laodelphax Striatellus In Suppressing Rice Defense,and Its Potential Application

Saliva,as the most important and closest medium in the interaction between insects and plants,plays an important role in helping insects to feed and regulating the defense response of host plants.The small brown planthopper Laodelphax striatellus（SBPH）is one of the most important rice pests in Asia.However,the salivary effector function of the SBPH is rarely studied.In this study,we take the saliva protein of the SBPH as the research object to analyze the role and mechanism of its regulation of plant defense response,which could enrich our understanding of the molecular mechanism of plant-insect interaction and provide targets and theoretical basis for guiding integrated pest management in the field.Previous studies found that salivary EF-hand Ca²⁺-binding protein（LsECP1）is necessary for the feeding,survival and reproduction of the SBPH on rice.This paper further explored the function and mechanism of regulating the defense response of rice.The subcellular localization showed that LsECP1 expressed in cytoplasm and nuclear of rice.Compared with the SBPH injected with GFP ds RNA and LsECP1 ds RNA,the accumulation of Ca²⁺in rice cells was significantly increased,which proved that the protein had the function of binding intracellular Ca²⁺in plants.Further respectively through RNA interference（RNAi）and haulm daub exogenous recombinant protein study two methods LsECP1 influence on rice defense reaction,silencing LsECP1 could significantly increase the contents of jasmonic acid（JA）,Isoleucine jasmonate（JA-Ile）and Hydrogen peroxide（H₂O₂）in rice,but had no effect on salicylic acid（SA）.Similarly,rice stalk application with LsECP1 could significantly inhibit the contents of JA,JA-Ile and H₂O₂induced by mechanical injury.These results indicated that LsECP1 could inhibit JA and H₂O₂signal transduction pathways in rice.In order to test whether this target could be applied to field SBPH control in the future,we obtained transgenic rice that could overexpress LsECP1 ds RNA.It was found that feeding on transgenic rice could significantly reduce the injury-causing effect of the SBPH.（1）The transcription level of LsECP1 in SBPH reared on transgenic rice plants was 50%to58%lower than that on wild type plants;（2）The feed intake of SBPH reared on transgenic rice was significantly reduced,leading to a significantly lower survival rate;（3）At the same time,the decrease of food intake also resulted in a significant decrease in the number of eggs.In conclusion,the effector LsECP1 inhibits the accumulation of defense signaling molecules related to rice resistance to insects by binding with excess intracellular Ca²⁺in rice,and thus enhances the toxicity of SBPH on host plants.However,transgenic rice overexpressing LsECP1 ds RNA showed obvious resistance to SBPH,showing a broad field application prospect.