The Analysis And Mechanism Of The Small Brown Planthopper Selecting Difference Between Infected Rice Plants(RSV/RBSDV)and Non-Infected Plants

The small brown planthopper(Laodelphax striatellus Fallen,SBPH)is an economically important pest,which causes severe damage to rice production in East Asian due to transmission of Rice stripe virus(RSV)and Rice black-streaked dwarf virus(RBSDV).The two viruses are transmitted by SBPH in a persistent,circulative-propagative manner.Somewhat differently,RSV can be transmitted from female adults to their progeny via eggs,while RBSDV has no transovarial transmission.In the process that insect horizontally transmits virus to plant host,it is involved in plant host orientation of insect vector,and the orientation behavior may be driven by olfaction.In the process of virus transmission,the host orientation behavior of insect is mainly driven by olfaction.In this context,the molecular basis of olfaction in SBPH is of particular interest.At present,the preference of WBPHs to rice stripe disease and black streaked dwarf strain is not clear.In this paper,the treatments for host orientation preference tests were designed as follows:(i)virus-free WBPH(adult/nymphs)for healthy plants or RSV-infected plants,(ii)RSV-infected WBPH(adult/nymphs)for healthy plants or RSV-infected plants,(iii)virus-free WBPH(nymphs)for healthy plants or RBSDV-infected plants,(iv)RBSDV-infected WBPH(nymphs)for healthy plants or RBSDV-infected plants,statistics and analysis of data.Then the expression of the olfactory related genes of the WBPH was analyzed,and the gene expression difference in RSV-infected and virusfree insects was screened,and the gene cloning and functional analysis of the olfactory receptor auxiliary receptor Orco were carried out.These studies laid the foundation for further explaining the mechanism of WBPH selection and the mechanism of disease/healthy plant improvement.1.Analysis of the selective difference of RSV-infected and virus-free WBPHs between infected rice plants and non-infected plantsIn this study,using a Y-shape olfactometer-based device,we tested the host preference of three types of macropterous WBPH adults for healthy or RSV infected rice plants.The results showed that virus-free WBPHs significantly preferred infected rice plants to healthy plants,whereas both the viruliferous WBPHs preferred healthy plants to infected plants.From these findings,we propose that plant viruses may alter host selection preference of vectors to enhance their spread.2.Analysis of the selective difference of RB-infected and virus-free WBPHs between infected rice plants and non-infected plantsRice black-streaked dwarf virus(RBSDV),an important rice virus,is transmitted by vector small brown planthopper(SBPH)in a persistent manner,but not transovarial transmission.In order to obtain viruliferous SBPH nymphs for relevant research,a simple and reliable method was developed,through allowing SBPH adults laying eggs on RBSDV-infected rice plants.The results showed the hatching nymphs on diseased plants could early acquire virus,and the virus was detected in 2nd-instar nymphs from the spawning method,which was earlier than insect feed on diseased plant.The average viruliferous rate of SBPH from the spawning method was 32.9%,which was not lower than the feeding diseased plant method.The novel method was very easy to operate and time-saving,facilitating the study on the interaction between RBSDV and SBPH nymphs(especially young 2nd-4th instar nymphs),such as,the effect of RBSDV on nymph development,host plant orientation preference of viruliferous nymph,identification of viral interacting protein in nymph,etc.3.Cloning and expression analysis of olfactory genes Orco of the small brown planthopperHere,we identified the gene that encodes olfactory receptor co-receptor(Orco)and analyzed its expression profiles in Rice stripe virus(RSV)-infected and RSV-free SBPH.It was found that LstrOrco shared high identity with other Orcos from different order insects.LstrOrco was mainly expressed in the head of SBPH,and its expression was significantly stimulated by RSV-infection.The behavioral bioassay revealed that viruliferous SBPH might have a stronger olfactory and seeking ability for rice than RSV-free insect.4.Functional analysis of Orco's olfactory genes in the small brown planthopperAfter silencing of LstrOrco expression,the olfaction and seeking behavior of nymphs for rice seedlings was significantly inhibited,mainly in the increase of the "no response"percent and the prolongation of the response time.These results suggested that Orco played an important role in olfactory signaling and seeking behavior of SBPH,which provided a basic for future development of olfactory-based agriculture pest management strategy.