CRYMASS

In the future, agriculture’s main challenge will be to increase crop production to feed the world’s growing population in a safe and sustainable manner. Between 20 and 40% of the world’s agricultural production is lost annually due to disease and pests. Synthetic pesticides have been extensively used but need to be limited because of their well-established negative impact on the environment and human health. Of all the strategies available, biopesticides offer a promising alternative means of pest management. Considered environmentally friendly, Bacillus thuringiensis kurstaki (Btk) is a bacterium that specifically targets pests by producing Cry toxins. It could be used as a sprayable pesticide or in genetically modified (GM) crops to express these toxins and make them resistant to the threat of lepidopteran larvae, one of the world’s most harmful pests. In targeted insect larvae, Cry toxins are thought to create pores that disrupt the gut epithelial membranes by interacting with specific receptors that are absent in non-targeted organisms. These pores allow the pathogen to enter the hemocoel, thereby killing the insect by sepsis in two or three days. Despite increased use of these genetically modified crops and Bt biopesticides, only a few studies have described the unintended effects of Cry toxins on non-target organisms. This project aims to characterize the impact of Cry toxin ingestion on Drosophila melanogaster, a powerful model for studying unintended effects. We had previously demonstrated that Cry toxin ingestion by adult Drosophila induces disruptions of the midgut homeostasis, leading to massive differentiation of intestinal stem cells into enteroendocrine cells instead of enterocytes. We suspected that this change in cell fate could be the consequence of an interaction between Cry toxins and cellular or extra-cellular proteins. We therefore combined immunoprecipitation with liquid chromatography-tandem mass spectrometry (IP–LC-MS/MS) to characterize the Cry toxin interactome in the Drosophila gut. Based on the results obtained, we focused on the role of the Cry-toxin interaction network in disrupting gut homeostasis. We achieved this by 1) using genetic approaches to make Drosophila strains gain or lose the function of identified midgut Cry-interactant, 2) defining the cellular and molecular processes disturbed by these complexes and 3) studying the fate of Cry toxins in the gut by localizing them at the tissue, cellular and subcellular levels in the Drosophila gut. Our results revealed that the interaction of Cry with two gut proteins is responsible for the diversion of ISC cell fate. Our work will be of major importance in understanding the mode of action of Cry toxins and will contribute to optimizing new strains that are less harmful for the environment and health without loss of effectiveness on devastating species.