Intraspecific variability of midgut Cys proteases in Colorado potato beetle fed different plant diets - A shotgun proteomics assessment

We observed earlier that the relative abundance of cathepsin L-like digestive Cys proteases in midgut extracts of the Colorado potato beetle (Leptinotarsa decemlineata Say) is strongly influenced by the plant diet. We also observed an intraspecific, population-dependent adjustment of the Cys protease complement in larvae ingesting different plants. Here we used a shotgun proteomics approach to compare the profiles of cathepsin L-like proteases in midgut extracts of potato, tomato and eggplant-fed larvae collected in Maryland, U.S.A., or near QuŽbec City, Canada. Fourth-instar larvae reared on potato were maintained for three more days on potato leaves, or transferred for three days on tomato or eggplant leaves. Their midgut proteins were extracted, and those proteins falling within the 25-33 kDa molecular weight range were submitted to mass spectrometry. Peptide mass spectra corresponding to cathepsin L enzymes were counted and classified based on a six-groups structural classification of the potato beetle cathepsin L family. In agreement with fluorimetric protease assays showing similar cathepsin L activities in potato-fed larvae regardless of their origin, potato-fed larvae from Maryland and QuŽbec exhibited similar cathepsin L proteomic profiles. By contrast, cathepsin L profiles in tomato- and eggplant-fed larvae strongly diverged depending on their origin, in line with protease assays indicating a strong decrease of cathepsin L activity in QuŽbec-collected larvae compared to a threefold increase in larvae from Maryland. These data indicate a population-dependent adaptation of the digestive protease complement in potato beetle larvae as a function of the plant diet.