Herbivorous insects feeding on plants expressing protease inhibitors compensate for the loss of digestive proteinase activity by producing novel proteinases. Here we assessed whether such compensatory responses represent a general, non-specific process or if distinct responses occur depending on the compounds found in the plant. As a model, digestive proteinases of the Colorado potato beetle (Leptinotarsa decemlineata Say) were monitored after feeding 3rd instars: (i) with ‘stressed’ potato plants expressing different sets of defense-related proteins; or (ii) with transgenic potato lines expressing different inhibitors of the cystatin superfamily. Larvae provided with the stressed plants compensated for the presence of defense proteins (incl. protease inhibitors) by modulating their digestive proteolytic complement, the changes observed varying with the stress exerted on the plant. Larvae provided with cystatin-expressing plants compensated for the loss of digestive proteinase activity by expressing novel cysteine proteinases, insensitive to the cystatins expressed. Noteworthy, compensation to the recombinant cystatins resulted in compensation to other cystatins of plant or animal origin. This apparent " cross-compensation " in larvae was not specific to cystatins, as the proregion of glycyl endopeptidase, a polypeptide active against the beetle’s cystatin-sensitive proteinases but structurally unrelated to cystatins, also showed decreased inhibitory potency against the cysteine proteinases of cystatin-adapted larvae. All in all, these observations document further the remarkable ability of herbivorous insects to adapt their digestive proteolytic machinery to the presence of protease inhibitors in plant tissues, either produced naturally in stressed plants or expressed ectopically in transgenic lines.
Species 1: Coleoptera Chrysomelidae Leptinotarsa decemlineata (Colorado potato beetle)
Keywords: proteinase inhibitors, digestive proteinases
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