The Mechanism Of Disulfide Isomerase From Small Brown Planthopper Saliva In Inducing Plant Immune Responses

Laodelphax striatellus(Fallén)is one of the main rice pests in Asia.In recent years,it has broken out in various rice areas in China,and its direct piercing and transmission of viral diseases have caused rice yield lost so much.SBPH is a kind of piercing sucking mouthparts insect.During its feeding on host plants,SBPH secretes a variety of salivary proteins into the host plant through its mouthparts,which triggers the interaction between SBPH and plants.Analysis of the mechanism of these salivary proteins can provide some ideas for elucidating the mechanism of insect-plant interaction,and guiding the scientific management of SBPH.However,the study on how SBPH saliva proteins mediate plant defense responses are still really rare.In this study,we have analyzed the salivary proteome of SBPH,and successfully identified a salivary protein Disulfide isomerase LsPDI1 from it.This salivary protein plays a very important role in the process of SBPH regulating the immune response of rice.We have studied it from the following aspects:(1)Molecular characteristics: After RT-qPCR analysis,we found that saliva LsPDI1 is highly expressed in all the growth stages when SBPH need to feed,and it is also highly expressed in the salivary glands and midgut of SBPH;.through PEGmediated transformation of rice protoplasts,we have observed that the salivary protein LsPDI1 is fully expressed in the nucleus and cytoplasm of plant cells,which indicates that LsPDI1 has an effect in various organelles and nuclei of plant cells.(2)Functional research: Using Nicotiana benthamiana transient expression system transiently expressed the salivary protein LsPDI1 of SBPH in leaves,which resulted in the outbreak of reactive oxygen species(ROS)in leaves and the massive death of plant cells;and we prove that it can also cause the death of plant cells in rice by using PEG-mediated transformation of rice protoplasts.(3)Mechanism: Through the toluidine blue special staining method,we found that the deposition of callose in the tobacco leaves increased significantly;Using RTq PCR to detect the expression levels of defense-related genes induced by LsPDI1 in N.benthamiana and rice,and the results show that LsPDI1 significantly increases the expression levels of related genes in the jasmonic acid(JA)signaling pathway;using HPLC-MS/MS detected the levels of JA,SA and JA-Ile in N.benthamiana leaves which transiently expressing LsPDI1,and we found that the contents of JA and JA-Ile were significantly increased,so we speculate that LsPDI1 induces the production of plant defense responses by activating the JA signaling pathway.(4)Homology analysis: We compared the amino acid sequence of LsPDI1 and the amino acid sequence of its homologous protein NlPDI in BPH saliva and SfPDI in WBPH saliva protein,and the results showed that thePDI protein is highly conserved among the three dominant species of planthoppers;transient expression of NlPDI and SfPDI,we found that they also cause plant ROS burst and cell death.In this paper,a new type of insect salivary elicitor,the salivary protein LsPDI1,is discovered.LsPDI1 enhances the plant’s defense response to pests by inducing plant active oxygen burst,plant cell death,and JA signaling pathway.This provides novel insights for studying the molecular mechanism of plant-insect interactions,and also provides new ideas for the integrated control of SBPH.