Transcriptomic and Expression Analysis of the Salivary Glands in White-Backed Planthoppers, Sogatella furcifera

Abstract

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth), is one of the serious rice pests because of its destructive feeding. The salivary glands of the WBPH play an important role in the feeding behaviour. Currently, however, very little is known about the salivary glands at the molecular level. We sequenced the salivary gland transcriptome (sialotranscripome) of adult WBPHs using the Illumina sequencing. A total of 65,595 transcripts and 51,842 unigenes were obtained from salivary glands. According to annotations against the Nr database, many of the unigenes identified were associated with the most studied enzymes in hemipteran saliva. In the present study, we identified 32 salivary protein genes from the WBPH sialotranscripome, which were categorized as those involved in sugar metabolism, detoxification, suppression of plant defense responses, immunity-related responses, general digestion, and other phytophagy processes. Tissue expression profiles analysis revealed that four of 32 salivary protein genes (multicopper oxidase 4, multicopper oxidase 6, carboxylesterase and uridine phosphorylase 1 isform X2) were primarily expressed in the salivary gland, suggesting that they played putative role in insect-rice interactions. 13 of 32 salivary protein genes were primarily expressed in gut, which might play putative role in digestive and detoxify mechanism. Development expression profiles analysis revealed that the expression level of 26 of 32 salivary protein genes had no significant difference, suggesting that they may play roles in every developmental stages of salivary gland of WBPH. The other six genes have a high expression level in the salivary gland of adult. 31 of 32 genes (except putative acetylcholinesterase 1) have no significant difference in male and female adult, suggesting that their expression level have no difference between sexes. This report analysis of the sialotranscripome for the WBPH, and the transcriptome provides a foundational list of the genes involved in feeding. Our data will be useful to investigate the mechanisms of interaction between the WBPH and the host plant.

Fig 1. Summary for the annotation of WBPH salivary gland transcriptome.

(A) Species distribution of best BLASTx hits of salivary gland transcriptome. (B) Gene Ontology (GO) classifications of WBPH salivary gland unigenes according to their involement in biological process, cellular component and molecular function.

Fig 2. KEGG pathway distributions of WBPH salivary gland unigenes.

The genes according to KEGG metabolic pathway involved was divided into five branches: A. Cellular processes; B. Environmental information processing; C. Genetic information processing; D. Metabolism; E. Organismal systems.

Fig 3. Transcript abundances of WBPH salivary protease genes in different tissues as measured by RT-qPCR.

SG: salivary gland; Head: head without salivary gland; Gut: gut; MT: malpighian tubule; RB: remaining body (without salivary gland, head, gut and malpighian tubule). (A) Sugar metabolism; (B) Detoxification and inhibition of plant defenses; (C) Immune related; (D) General digestion; (E) Other proteins.

Fig 4. Developmental stage- and sex-specific expression of salivary protease genes in WBPH salivary gland by RT-qPCR.

Total RNA was extracted from the salivary gland of 2^nd-3^rd instar nymph, 4^th-5^th instar nymph, female and male adult. (A) Sugar metabolism; (B) Detoxification and inhibition of plant defenses; (C) Immune related; (D) General digestion; (E) Other proteins.