Screening And Expression Of Candidate Odorant Binding Protein Related To Host Selection Of Encarsia Formosa Against Bemisia Tabaci

Encarsia formosa Gahan is an important parasitic natural enemy of Bemisia tabaci(Gennadius),a super pest all over the world.It has been widely used in biological control of whiteflies on vegetables and ornamental plants in greenhouses,and has become an international model of biological control for pests.The previous studies described that the E.formosa was attracted by ?-myrcene,?-ocimene,?-caryophyllene,and ?-humulene,which are volatiles released by Tomato Yellow Leaf Curl Virus(TYLCV)-infected tomato plants;and the E.formosa wasps were found to significantly prefer the B.tabaci biotype Q instead of B.tabaci biotype B on TYLCV-infected tomato plants,indicating its selectivity to different biotypes of B.tabaci and virus-infected states of plant.However,the mechanism by which E.formosa recognizes chemical volatiles and prefers different host at the molecular level remains unknown.To address this problem,the following studies were carried out.First,E.formosa antennal transcriptome was conducted by Next-generation platform.Second,39 odorant binding proteins(OBPs)from the former database were identified and analyzed by phylogenetic tree.Third,the transcript expression levels of OBPs in different tissues,developmental stages of E.formosa and in different odor environments were investigated by real-time quantitative polymerase chain reaction(q PCR).The candidate OBP genes that might be involved in the host location and selection of B.tabaci B and Q were obtained.This work provides a molecular basis for functional studies on these OBPs,and would be helpful for the demonstration and manipulation of the host-location behaviors of E.formosa parasitizing the B.tabaci whiteflies.1.Construction of antennal transcriptome and the annotation of unigenes in E.formosa We obtained 66,632 unigenes from antennae transcriptomic architecture of E.formosa,of which the N50 length was up to 1,623 bp,and 11,990(18%)exceeded 1000 bp in length.19,473(29.2%)unigenes were functionally annotated,including 17,719 NR,7,884 GO,5,340 COG,9,515 Swiss prot and 6,634 KEGG.Compared with NR database,58.12% of unigenes had the highest similarity with Nasonia vitripennis.2.Cloning,classification and phylogenetic analysis of OBPs in E.formosa Based on the gene annotation of the transcriptome data,39 OBPs were identified and analyzed by multiple sequence alignment,motif analysis and phylogenetic analysis.Four to six Cysteine and six motifs were found among Efor OBPs.These OBPs are about 400 bp long and can be divided into two categories including 31 Classic OBPs and 8 Minus-C OBPs.3.The relative expression and induced expression of OBPs in E.formosa The tissue-and stage-specific expression profiles of 39 putative OBP genes among different tissues and different stages of E.formosa were investigated by q PCR.It was confirmed that 32 OBP genes were enriched in antennae,2 OBPs genes named OBP8 and OBP33 were enriched in body,and 5 OBPs expressed similarly in antennae and body.In addition,4 OBPs(OBP13,OBP24,OBP30,and OBP39)were highly expressed at pupa stage,as well as 32 OBPs highly expressed at adult stages,especially in 6-hour-age adults after eclosion,and 3 OBPs expressed similarly in adult and pupa.After that,E.formosa was immersed in the odor environment of VQ(B.tabaci biotype Q feeding on the TYLCV-infected tomato)and VB(B.tabaci biotype B feeding on the TYLCV-infected tomato).There were significant differences in the expression of 21 OBPs genes between VQ and VB treatments.Eight candidate key genes,OBP10,OBP11,OBP21,OBP22,OBP26,OBP27,OBP29 and OBP31,were obtained from the intersection of the four screening conditions of high expression of OBPs in antennae,high expression of OBPs in adult stage,OBPs with FPKM value more than 100,and OBPs with significant difference between VQ and VB.It is speculated that these eight genes may play an important role in different selection behaviors of B.tabaci biotype Q and biotype B.