Salivary gland transcriptomics of the cotton aphid Aphis gossypii and comparative analysis with other sap-sucking insects.

Aphids are sap-sucking insects responsible for crop losses and a severe threat to crop production. Proteins in the aphid saliva are integral in establishing an interaction between aphids and plants and are responsible for host plant adaptation. The cotton aphid, Aphis gossypii (Hemiptera: Aphididae) is a major pest of Gossypium hirsutum. Despite extensive studies of the salivary proteins of various aphid species, the components of A. gossypii salivary glands are unknown. In this study, we identified 123,008 transcripts from the salivary gland of A. gossypii. Among those, 2933 proteins have signal peptides with no transmembrane domain known to be secreted from the cell upon feeding. The transcriptome includes proteins with more comprehensive functions such as digestion, detoxification, regulating host defenses, regulation of salivary glands, and a large set of uncharacterized proteins. Comparative analysis of salivary proteins of different aphids and other insects with A. gossypii revealed that 183 and 88 orthologous clusters were common in the Aphididae and non-Aphididae groups, respectively. The structure prediction for highly expressed salivary proteins indicated that most possess an intrinsically disordered region. These results provide valuable reference data for exploring novel functions of salivary proteins in A. gossypii with their host interactions. The identified proteins may help develop a sustainable way to manage aphid pests.

Identification of salivary proteins of the cowpea aphid Aphis craccivora by transcriptome and LC-MS/MS analyses.

Aphid salivary proteins mediate the interaction between aphids and their host plants. Moreover, these proteins facilitate digestion, detoxification of secondary metabolites, as well as activation and suppression of plant defenses. The cowpea aphid, Aphis craccivora, is an important sucking pest of leguminous crops worldwide. Although aphid saliva plays an important role in aphid plant interactions, knowledge of the cowpea aphid salivary proteins is limited. In this study, we performed transcriptomic and LC-MS/MS analyses to identify the proteins present in the salivary glands and saliva of A. craccivora. A total of 1,08,275 assembled transcripts were identified in the salivary glands of aphids. Of all these assembled transcripts, 53,714 (49.11%) and 53,577 (49.48%) transcripts showed high similarity to known proteins in the Nr and UniProt databases, respectively. A total of 2159 proteins were predicted as secretory proteins from the salivary gland transcriptome dataset, which contain digestive enzymes, detoxification enzymes, previously known effectors and elicitors, and potential proteins whose functions have yet to be determined. The proteomic analysis of aphid saliva resulted in the identification of 171 proteins. Tissue-specific expression of selected genes using RT-PCR showed that three genes were expressed only in the salivary glands. Overall, our results provide a comprehensive repertoire of cowpea aphid salivary proteins from the salivary gland and saliva, which will be a good resource for future effector functional studies and might also be useful for sustainable aphid management.