Identification and expression profile analysis of odorant binding protein and chemosensory protein genes in Bemisia tabaci MED by head transcriptome

Abstract

Odorant binding proteins (OBPs) and chemosensory proteins (CSPs) of arthropods are thought to be involved in chemical recognition which regulates pivotal behaviors including host choice, copulation and reproduction. In insects, OBPs and CSPs located mainly in the antenna but they have not been systematically characterized yet in Bemisia tabaci which is a cryptic species complex and could damage more than 600 plant species. In this study, among the 106,893 transcripts in the head assembly, 8 OBPs and 13 CSPs were identified in B. tabaci MED based on head transcriptomes of adults. Phylogenetic analyses were conducted to investigate the relationships of B. tabaci OBPs and CSPs with those from several other important Hemipteran species, and the motif-patterns between Hemiptera OBPs and CSPs were also compared by MEME. The expression profiles of the OBP and CSP genes in different tissues of B. tabaci MED adults were analyzed by real-time qPCR. Seven out of the 8 OBPs found in B. tabaci MED were highly expressed in the head. Conversely, only 4 CSPs were enriched in the head, while the other nine CSPs were specifically expressed in other tissues. Our findings pave the way for future research on chemical recognition of B. tabaci at the molecular level.

Fig 1. Percentage of homologous hits of the B. tabaci transcripts to other insect species.

The B. tabaci transcripts were searched by BLASTx against the non-redundancy protein database with a cutoff E-value 10⁻⁵.

Fig 2. Analyses of head transcriptome of B. tabaci MED.

(A) Gene Ontology (GO) analysis for the transcriptomic sequences. (B) Eukaryotic Ortholog Groups of proteins (KOG) annotation of the transcriptome. (C) Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation of the transcriptome.

Fig 3. Alignment of the identified B. tabaci OBPs.

Full-length amino acid sequences of B. tabaci MED OBPs are aligned by Clustal X 2.1. Black boxes show conserved cysteines. The conserved Cys residues are indicated.

Fig 4. Alignment of the identified B. tabaci CSPs.

Full-length amino acid sequences of B. tabaci MED CSPs are aligned by Clustal X 2.1. Black boxes show conserved cysteines. The conserved Cys residues are indicated.

Fig 5. Phylogenetic relationship of candidate OBP proteins from B. tabaci MED and other hemipteran insects.

The tree was constructed by MEGA 5.1 program using the neighbor-joining method with the Bootstrapping model by 1000 replication.

Fig 6. Phylogenetic relationship of candidate CSP proteins from B. tabaci MED and other hemipteran insects.

The tree was constructed by MEGA 5.1 program using the neighbor-joining method with the Bootstrapping model by 1000 replication.

Fig 7. Motif analysis of Hemiptera OBPs and CSPs.

Parameters used for motif discovery were: minimum width = 6, maximum width = 10, maximum number of motif to find = 8. The upper parts in (A, B) listed the eight motifs discovered in the Hemiptera OBPs and CSPs, receptively.

Fig 8. B. tabaci MED OBPs and CSPs transcript levels in different tissues as measured by RT-qPCR.

FHe: female head; MHe: male head; Th: thorax; Ab: abdomen; Le: leg; Wi: wing. The expression levels were estimated using 2^{- Δ ΔCt} method. Standard error for each sample is represented by error bar and the different letters (a, b, c, d, e) above each bar denote significant differences (p < 0.05).