Characterization of Antennal Chemosensilla and Associated Chemosensory Genes in the Orange Spiny Whitefly, Aleurocanthus spiniferus (Quaintanca)

Abstract

The insect chemosensory system plays an important role in many aspects of insects' behaviors necessary for their survival. Despite the complexity of this system, an increasing number of studies have begun to understand its structure and function in different insect species. Nonetheless, the chemosensory system in the orange spiny whitefly Aleurocanthus spiniferus, as one of the most destructive insect pests of citrus in tropical Asia, has not been investigated yet. In this study, the sensillum types, morphologies and distributions of the male and female antennae of A. spiniferus were characterized using scanning electron microscopy. In both sexes, six different sensilla types were observed: trichodea sensilla, chaetica sensilla, microtrichia sensilla, coeloconic sensilla, basiconic sensilla, and finger-like sensilla. Moreover, we identified a total of 48 chemosensory genes, including 5 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 3 sensory neuron membrane proteins (SNMPs), 6 odorant receptors (ORs), 8 gustatory receptors (GRs), and 14 ionotropic receptors (IRs) using transcriptome data analysis. Tissue-specific transcriptome analysis of these genes showed predominantly expression in the head (including antennae), whereas CSPs were broadly expressed in both head (including the antennae) and body tissue of adult A. spiniferus. In addition, the expression profiling of selected chemosensory genes at different developmental stages was examined by quantitative real time-PCR which was mapped to the transcriptome. We found that the majority of these genes were highly expressed in adults, while AspiORco, AspiGR1, AspiGR2, and AspiIR4 genes were only detected in the pupal stage. Together, this study provides a basis for future chemosensory and genomic studies in A. spiniferus and closely related species. Furthermore, this study not only provides insights for further research on the molecular mechanisms of A. spiniferus-plant interactions but also provides extensive potential targets for pest control.

Keywords: Aleurocanthus spiniferus; antennal sensilla; chemosensory genes; expression patterns; transcriptome.

FIGURE 1

The types of sensilla present on A. spiniferus antennae. (A) Female antenna. (B) Grooved surface richodea sensilla (C) Chaetae sensilla. (D) Figure-like sensilla. (E) Basiconic sensilla. (F) Basiconic sensilla. (G) Coeloconic and microtrichia sensilla.

FIGURE 2

Phylogenetic analysis of putative odorant-binding proteins (OBPs) of A. spiniferus. The phylogenetic tree was built using OBP sequences from whitefly species (Btab, Bemisia tabaci; Aspi, A. spiniferus), aphid species (Apis, Acyrthosiphon pisum; Mper, Myzus persicae; Agos, Aphis gossypii; Psal, Pterocomma salicis; Agly, Aphis glycines; Mdir, Metopolophium dirhodum; Mvic, Megoura viciae; Bbra, Brevicoryne brassicae; Lery, Lipaphis erysimi; Afab, Aphis fabae; Acra, Aphis craccivora; Tsal, Tuberolachnus salignus; Dpla, Drepanosiphum platanoidis; Nrib, Nasonovia ribisnigri; Rpad, Rhopalosiphum padi), plant hoppers (Sfur, Sogatella furcifera; Nlug, Nilaparvata lugens), and plant bugs (Aluc, Apolygus lucorum; Alin, Adelphocoris lineolatus).

FIGURE 3

Phylogenetic analysis of putative chemosensory proteins (CSPs) of A. spiniferus. The phylogenetic tree was built using CSP sequences from whitefly species (Btab, B. tabaci; Aspi, A. spiniferus), aphid species (Apis, A. pisum; Agos, A. gossypii), plant hoppers (Sfur, S. furcifera; Nlug, N. lugens) and plant bugs (Aluc, A. lucorum; Alin, A. lineolatus).

FIGURE 4

Phylogenetic analysis of putative sensory neuron membrane proteins of A. spiniferus.

FIGURE 5

Phylogenetic analysis of putative odorant receptors (ORs) of A. spiniferus. The phylogenetic tree was built using OR sequences from whitefly specie (Aspi, A. spiniferus) and aphid species (Apis, A. pisum; Rpad, R. padi; Agos, A. gossypii).

FIGURE 6

Phylogenetic analysis of putative gustatory receptors (GRs) of A. spiniferus. The phylogenetic tree was built using GR sequences from whitefly specie (Aspi, A. spiniferus), aphid species (Apis, A. pisum; Rpad, R. padi; Agos, A. gossypii) and fly (Drosophila melanogaster).

FIGURE 7

Phylogenetic analysis of putative ionotropic receptors (IRs) of A. spiniferus. The phylogenetic tree was built using IR sequences from whitefly specie (Aspi, A. spiniferus), aphid species (Apis, A. pisum; Rpad, R. padi; Agos, A. gossypii) and fly (Drosophila melanogaster).

FIGURE 8

Quantitative real-time polymerase chain reaction (qPCR)-based expression profiling of selected chemosensory genes in different developmental stages of A. spiniferus.

FIGURE 9

Expression profiles of chemosensory genes in different tissues. (A) Heatmap of chemosensory genes in the antennal transcriptome. Significance means an absolute value of log₂Ratio ≥ 1 and FDR < 0.05. (B) Validation of selected chemosensory genes in different tissues by qPCR.