Leaf beetles occur worldwide; some of them are even economically important pests of agriculture. They raise broad ecological interest because of their host plant preferences and varying modes of life. Their larvae have developed an impressive repertoire of toxins and repellents to defend themselves against predators. Upon attack, the larvae discharge small droplets from specialized glandular reservoirs on their back (e.g. Chrysomelapopuli). The reservoirs represent “bioreactors” performing all late reactions of the toxin-production, starting from plant-derived or de novo synthesized glucosides. The import of the plant-derived glucosides relies on a sophisticated transport system. Physiological studies revealed a functional network of transporters guiding the plant derived glucosides through the larval body into the defensive system. As transporters usually represent trans-membrane proteins, we developed a protocol for the isolation and identification of these proteins from membranes of the defensive system. After cell lysis and differential centrifugation proteins were separated by SDS-page followed by in-gel digestion and nanoLC-HDMSE analysis. From more than 2000 proteins of glandular tissue, bioinformatic criteria revealed several ABC-transporters and candidates from the solute carriers (SLC) that mediate facilitative diffusion of their sub­strates. Expression analysis of these candidate sequences revealed for some of them high expression in the defensive glands compared to other larval tissues. A subsequent lack-of-function screening by using RNAi revealed in particular one ABC-transporter and an SLC2-candidate being involved in the uptake of salicin from hemolymph into the secretory cell. Heterologous expression of these transporters in frog oocytes confirmed salicin as a substrate. A functional model of the transport network in the leaf beetle C. populi has be developed and will be presented.

Strauss, W. Boland, A. Burse. ABC transporter functions as a pacemaker for the sequestration of plant glucosides in leaf beetles. (2013) eLife http://dx.doi.org/ 10.7554/eLife.01096 .