Effects Of Rice Stripe Virus Infection On The Host-seeking Behavior Of Laodelphax Striatellus By Regulating Odorant Binding Proteins

Laodelphax striatellus(Hemiptera:Delphacidae),the small brown planthopper(SBPH),is a notorious rice pest in East Asia.It damages the host by feeding on the phloem and transmitting virus particles,including rice black-streaked dwarf virus(RBSDV)and rice stripe virus(RSV).RSV is transmitted by the SBPH in a persistent-propagative manner.SBPH relies on chemosensory perception for seeking the host,courtship,selecting oviposition sites and spreading virus particles.In chemosensory processes,the odorant binding protein(OBP)is an essential element for filtering,binding and transporting hydrophobic odorant molecules to the specific receptors.Virus-host interaction is a central topic for future research.However,the effects of RSV infection on the host-seeking behavior in SBPH have not been fully elucidated.In this paper,we examined the behavioral responses of RSV-infected and RSV-free SBPH to rice,respectively,through the H-shaped olfactometer.We identified multi-gene chemosensory families from the transcriptome of SBPH olfactory organs and analyzed their expression patterns in male and female tissues Finally,we validated the relative expression of OBPs of RSV-infected and RSV-free SBPH by quantitative real-time PCR.The results were as follows.(1)We first revealed that RSV particles localized in the antennaes from RSV-infected SBPH by Laser scanning confocal microscopy(LSCM).Notably,RSV particles were found to accumulate in the entire flagellum and sensilla placodea of pedicel.Furthermore,we found that RSV infection had an inhibitory effect on the host-localization behavior of SBPH by the H-shaped olfactometers.RSV-infected SBPH showed obvious loss of rice plant-seeking ability.(2)Among the chemosensory genes,14 odorant-binding proteins(OBPs)were identified and annotated in SBPH olfactory organs.Based on expression profile and phylogenetic analysis,LsOBP1,2,5,6,7,10 showed an antennae-enriched expression pattern.Five OBPs(LsOBP3,4,9,11 and 12)showed high mRNA levels in heads(without antennae),while LsOBP13 was highly expressed in legs.Moreover,sex-specific expression of chemosensory genes was apparent.For instance,LsOBP4,11,and 15 were expressed at higher levels in female tissues.LsOBP3,7,8,and 10 were expressed at higher levels in males than females.(3)OBPs(LsOBP2,3,4,5) were expressed at lower mRNA levels in heads(with antennae)of RSV-infected SBPH by q-PCR.Transient gene silencing was used to reduce LsUBI expression,which caused a significant reduction in detectable RSV loads and viral RSV expression levels in the antennae of RSV-infected SBPH.However,LsOBP3 highly expressed were accompanied by the downregulation of the expression of RSV.These results further suggested that RSV infection with SBPH inhibited the expression of LsOBP3.Finally,repression of LsOBP3 significantly downregulated the relative responses to rice seeding for RSV-free SBPH by RNAi and the H-shaped olfactometers.The results revealed that the OBP3-deficient SBPH were partly anosmic and lost some of their ability to locate rice plants Therefore,it could speculate that RSV infection inhibits the expression of LsOBP3,resulting in a weakened host localization ability in SBPH.