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BackgroundInsect odorant-binding proteins (OBPs) are a class of small molecular weight soluble proteins. In the past few years, OBPs had been found to work as carriers of ligands and play a crucial role in olfaction and various other physiological processes, like immunity. A subset of insect OBPs had been found to be expressed differently and play a function in immunity of fungal infection. However, there are few studies on the role of OBPs in immunity of bacterial infection.MethodsTo identify the immune-related OBPs of Plagiodera versicolora after infected by Pseudomonas aeruginosa, we determined the mortality of P. versicolora to P. aeruginosa and selected the time point of 50% mortality of larvae to collect samples for RNA-seq. RNAi technology was used to investigate the function of immune-related OBPs after P. aeruginosa infection.ResultsRNA-seq data shows that PverOBP18 gene significantly up-regulated by 1.8-fold and further RT-qPCR affirmed its expression. Developmental expression profile showed that the expression of PverOBP18 was highest in the pupae, followed by the female adults, and lower in the 1st-3rd larvae and male adults with lowest in eggs. Tissue expression profiling showed that PverOBP18 was dominantly expressed in the epidermis. RNAi knockdown of PverOBP18 significantly reduced the expression of bacterial recognition receptor gene PGRP and antibacterial peptide gene Attacin and reduced the resistance of P. versicolora to P. aeruginosa infection.ConclusionOur results indicated that PverOBP18 gene increased the pathogen resistance of P. versicolora by cooperating with the immune genes and provided valuable insights into using OBPs as targets to design novel strategies for management of P. versicolora.

Double-stranded RNA (dsRNA)-degrading enzyme (dsRNase) is one of the negative factors influencing the RNA interference (RNAi) effect in Colorado potato beetle (CPB). We have previously shown that plastid-mediated RNAi (PM-RNAi) can be utilized to control CPB. In this study, we aimed to test whether silencing dsRNase could increase the RNAi effect in CPB via PM-RNAi. We generated transplastomic potato (Solanum tuberosum) plants expressing dsRNA targeting shibire (dsSHI) of CPB. St-dsSHI plants (transplastomic plants expressing dsSHI) showed much less potent RNAi response than transplastomic potato plants expressing dsRNAs targeting CPB Shrub (St-dsSHR) or β-Actin (St-dsACT), two CPB-resistant transplastomic lines generated previously. The three types of transplastomic lines have weak (St-dsSHI), moderate (St-dsSHR) and strong (St-dsACT) resistant levels to CPB. Treatment with in vitro-synthesized dsdsRNase1/2 (a fusion dsRNA targeting dsRNase1 and dsRNase2 of CPB) led to enhanced suppression of dsRNase1 and dsRNase2 in CPB larvae fed with St-dsSHI plants and dsRNase2 in CPB larvae fed with St-dsSHR plants. St-dsSHR or St-dsSHI plants showed significantly reduced CPB larva weight or damaged area by CPB feeding. These results demonstrate that dsRNase-silencing approach could improve the effect of PM-RNAi when the silencing of target genes has weak or moderate strength of the insecticidal effects. The findings provide a new proof-of-concept to enhance crop resistance to insect herbivores to via an “RNAi-of-RNAi” approach. [ABSTRACT FROM AUTHOR]