Tissue-specific profiling of membrane proteins in the salicin sequestering juveniles of the herbivorous leaf beetle, Chrysomela populi

Sequestration of plant secondary metabolites is a detoxification strategy widespread in herbivorous insects including not only storage, but also usage of these metabolites for the insects' own benefit. Larvae of the poplar leaf beetle Chrysomela populi sequester plant-derived salicin to produce the deterrent salicylaldehyde in specialized exocrine glands. To identify putative transporters involved in the sequestration process we investigated integral membrane proteins of several tissues from juvenile C. populi by using a proteomics approach. Computational analyses led to the identification of 122 transport proteins in the gut, 105 in the Malpighian tubules, 94 in the fat body and 27 in the defensive glands. Among these, primary active transporters as well as electrochemical potential- driven transporters were most abundant in all tissues, including ABC transporters (especially subfamilies B, C and G) and sugar porters as most interesting families facilitating the sequestration of plant glycosides. Whereas ABC transporters are predominantly expressed simultaneously in several tissues, sugar porters are often expressed in only one tissue, suggesting that sugar porters govern more distinct functions than members of the ABC family. The inventory of transporters presented in this study provides the base for further functional characterizations on transport processes of sequestered glycosides in insects