Abstracts (first author)
Chrysomelina leaf beetles profit from widely exploiting their host plants: ABC transporters are involved in the sequestration of poisonous phytochemicals
The ubiquitous consumption of plants by insect herbivores requires in many cases detoxification of noxious phytochemicals. One of the most ingenious detoxification strategies widespread in insects is sequestration which involves uptake, transfer and concentration into specialized tissues. Frequently, sequestered compounds are not only stored securely by the insects, but further; insects evolved the ability to use an overwhelming diversity of exogenous compounds for their own benefit within the competitive interactions in natural ecosystems, like for repelling insects’ enemies. Here, we report the first example of a transport protein crucial for the translocation of phytochemicals in insects. The transporter, referred to here as CpMRP, belongs to the ATP binding cassette (ABC) transporter family and functions in the defensive exocrine glands of juvenile poplar leaf beetle, Chrysomela populi, for shuttling plant derived metabolites into deterrent secretions. Silencing of CpMRP in vivo by using RNAi creates a defenseless phenotype which indicates its key function also for the secretion process. Our analyses of the transport activity suggest that involving a broad-spectrum carrier in the sequestration of phytochemicals may be advantageous for insects to affiliate alternative host plants. Indeed, we identified transporter sequences highly similar to CpMRP in the larval glands of a related Chrysomelina leaf beetle species which forms allopatric populations and shifts hosts between chemically different plant families. This demonstrates the importance of the substrate flexibility provided by ABC transporters to avoid feeding specialization and host-derived chemical defense leading to an evolutionary dead end. Moreover, ancestral species of C. populi synthesizing defensive compounds endogenously already possess in their glands CpMRP-similar proteins which shed new light on the evolution of sequestration in the taxon Chrysomelina.