Comparative Sialotranscriptome And Antennal Transcriptome Analysis Of The Cicada Subpsaltria Yangi (Hemiptera: Cicadidae)

The cicada Subpsaltria yangi(Hemiptera: Cicadidae)is a rare Chinese species of conservation concern,feedind on vascular fluids of its host plants with piercing-sucking mouthparts.Shaanxi populations of S.yangi feed on Ziziphus jujuba Mill.var.spinosa(Bunge)Hu ex H.F.Chow(Rhamnaceae).In contrast,the population occurring in the Helan Mountains,Ningxia Hui Nationality Autonomous Region,China has shifted to a chemically divergent host,Ephedra lepidosperma C.Y.Cheng(Ephedraceae).E.lepidosperma is an endemic species to the Helan Mountains,and is a medicinal plant containing ephedrine and pseudoephedrine,which can stimulate the nerve system of animals.However,little is known about mechanisms underlying how to select and shift the host plants for S.yangi.In this study,we employed a transcriptome approach based on transcriptome sequencing of salivary glands and antennae in Shaanxi and Ningxia populations of S.yangi,respectively.We constructed expression patterns of differentially expressed genes(DEGs)and detected digestion-and detoxification-related genes that are differentially expressed in the populations of S.yangi feeding on two kinds of host-plants.These DEGs may help to elucidate molecular mechanisms of host-plant adaptation in S.yangi.Also,we identified the olfactory gene repertoire essential for olfactory processes such as feeding and/or oviposition of S.yangi.Better understanding of the odor-processing genes in this piercing-sucking species could help to clarify the mechanism of host selection for feeding and/or oviposition behaviors in phytophagous insects.Results and conclusions are as follows:1.In total,66.7 G clean reads were abtained from the salivary glands of S.yangi,and with the assembly of these clean reads,there were 180,765 unigenes generated.The prediction of SSRs showed that 48,173 sequences containing 64,395 simple sequence repeats were identified,with 11,976 sequences containing more than one SSR.Pairwise comparisons of three populations showed 2,868 DEGs,and in HL vs HC and HL vs FX indicated the presence of 2,208 and 659 DEGs present between populations utilizing E.lepidosperma and Z.jujuba,respectively.In FX vs HC,632 DEGs were found between two populations feeding on same host plant Z.jujuba.Combining the results of GO and KEGG enrichment and unigenes annotation,38 DEGs and 21 up-regulated genes related to digestion and detoxication were identified respectively in two pairwise comparisons among cicadas using different hosts.Our results suggest that the HL population of S.yangi succeeded in shifting to feed on E.lepidosperma through differential regulation of genes related to digestion and detoxification.This study provides new information on the molecular mechanisms of diet differentiation in a rare cicada species of conservation concern.2.In total,13 complete cytoplasmic GSTs were identified from the salivary gland transcriptome of S.yangi.Based on the sequence similarity and phylogenetic tree,these GSTs were categorized into five classes,i.e.,6,4,1,1 and 1 belong to classes Sigma,Delta,Zeta,Theta,and Epsilon,respectively.No GST was found belonging to the Omega class.The prediction of chemicophysical properties showed that the aliphatic indexes of all 13 GSTs were more than 80 and they all were predicted to be hydrophilic proteins which have no transmembrane region.Only Sy GSTd4 is predicted to be positioned to extracellular with a signal peptide,and the remaining 12 GSTs are predicted to be non-secretory cytoplasmic proteins.The predicted secondary structure,tertiary structure and catalytic sites of GSTs provide informative data for further exploration of the detoxication function played by GSTs in S.yangi.3.In total,we identified ten unigenes encoding putative odorant-binding proteins(OBPs),ten chemosensory proteins(CSPs),eight sensory neuron membrane proteins(SNMPs),seven gustatory receptors(GRs),29 odorant receptors(ORs)and 13 ionotropic receptors(IRs)in antennal transcriptome of S.yangi.We used q RT-PCR to examine the expression profile of eight genes sets in various organs.We found that OBPs were mainly expressed in olfactory organs such as antenna and mouthpart,suggesting a vital role of OBPs in olfactory recognition process.ORs were highly expressed in the head and antenna,indicating that they connect binding proteins with olfactory sensory neurons(OSNs)and conduct olfactory signal transduction.CSPs were mainly expressed in almost all olfactory organs and non-olfactory organs,showing that their functions in odor transport are not restricted.Our results make it possible for future research of the olfactory system of S.yangi at the molecular level,and provide important bases for elucidation of the molecular mechanisms and evolution of insect chemosensation.