Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2016
Publication Date: 8/2/2016
Publication URL: https://handle.nal.usda.gov/10113/5399134
Citation: Van Ekert, E., Chauvigne, F., Finn, R.N., Mathew, L.G., Hull, J.J., Cerda, J., Fabrick, J.A. 2016. Molecular and functional characterization of Bemisia tabaci aquaporins reveals the water channel diversity of hemipteran insects. Insect Biochemistry and Molecular Biology. 77:39-51.

Interpretive Summary: The sweetpotato whitefly is a global insect pest of food, fiber, and ornamental crops. Whiteflies damage crops by feeding directly on plant sap, transmitting plant disease viruses, and by promoting growth of microbes on plant material due to the excretion of large volumes of high sugar content waste. A number of adaptations allow this pest to overcome physiological challenges, including 1) the ability to regulate water stress on internal structures after ingesting large quantities of a low nutrient, sugar-rich liquid diet; 2) the ability to avoid or prevent dehydration and desiccation; and 3) to be adapted for survival in hot environments. ARS scientists at Maricopa, AZ and collaborators identified and characterized eight whitefly aquaporin water channel proteins that enable efficient use, regulation, and conservation of water in this pest. Each protein has unique expression profile, cellular localization, and/or substrate preference. Our comparison of these proteins with other insect aquaporins further reveals that whiteflies and other related insects lost a group of genes known to function in the transport of glycerol, but have compensated for this by duplicating a unique class of channels known as entomoglyceroporins. These results reveal new information regarding the role of aquaporins in the maintenance of nutrient and water homeostasis in whiteflies and point to novel targets for pest control.

Technical Abstract: The Middle East-Asia Minor 1 (MEAM1) whitefly, Bemisia tabaci (Gennadius) is an economically important pest of food, fiber, and ornamental crops. This pest has evolved a number of adaptations to overcome physiological challenges, including 1) the ability to regulate osmotic stress between gut lumen and hemolymph after imbibing large quantities of a low nutrient, sugar-rich liquid diet; 2) the ability to avoid or prevent dehydration and desiccation, particularly during egg hatching and molting; and 3) to be adapted for survival in elevated thermal environments. One superfamily of proteins involved in the maintenance of fluid homeostasis in many organisms includes the aquaporins, which are integral membrane channel proteins that aid in the rapid flux of water and other small solutes across biological membranes. Here, we show that B. tabaci has eight aquaporins (BtAqps), of which seven belong to the classical Aqp4-related grade of channels, including Bib, Drip, Prip, and Eglps and one that belongs to the unorthodox grade of Aqp12-like channels. B. tabaci has further expanded its repertoire of water channels through the expression of three BtDrip2 amino-terminal splice variants, while other hemipteran species express amino- or carboxyl-terminal isoforms of Drip, Prip, and Eglps. Each BtAqp has unique transcript expression profiles, cellular localization, and/or substrate preference. Our phylogenetic data reveal that hemipteran insects lost the classical glp genes, but have compensated for this by duplicating the eglp genes early in their evolution to comprise at least three separate clades of glycerol transporter.