Many plants defend themselves against attacks from plant-eating animals and insects by releasing the highly poisonous compound cyanide (HCN). Some insects and mites can thrive on toxic cyanogenic plants,which has puzzled the scientific community for over a century. An international team lead by Thomas van Leeuwen of the Institute for Biodiversity and Ecosystem Dynamics (IBED), shows in a recent publication in the new eLIFE journal that moths and mites can detoxify these chemical using a special gene taken from bacteria.
The production of dedicated compounds to deter animals and insects is a common strategy used by plants for their self-defence. For instance, Cassava is a key source of nutrients in sub-Saharan Africa, but also contains the cyanogenic glucoside linamarin (a cyanide-enriched sugar molecule). This compound makes the Cassava plant highly toxic to animals and humans if eaten in an unprocessed form.
Van Leeuwen and his colleagues first focused on the cosmopolitan pest spider mite Tetranychus urticae, which they exposed to toxic cyanogenic plants. After cultivating mites for 30 generations on toxic plants in the lab, the team identified a previously uncharacterized mite gene that increases its expression after the mites adapted to the toxins. Surprisingly, bacteria, butterflies and moths share the same gene, which was duplicated or triplicated in moths that thrive on these cyanogenic plants. By studying their ‘tree of life’ (known as a phylogenetic analysis) the researchers showed that mites and moths hijacked the gene from bacteria through a process of horizontal gene transfer. Functional analysis revealed that the transferred gene encodes for a special enzyme that converts toxic cyanide to a non-toxic product that resembles an amino acid.
The bacterial enzyme which transferred horizontally to the genomes of ancestral moths and mites allows these herbivores to exploit toxic plants, in a remarkable coalition of two kingdoms against another. Solving this enigma is a great step forward in understanding how plant-herbivore interactions evolve over time and it simultaneously underlines the importance of horizontal gene transfer in the evolution of complex species (eukaryotes).
Wybouw, N., Dermauw, W., Tirry, L., Stevens, C., Gric, M., Feyereisen, R., Van Leeuwen, T., A gene horizontally transferred from bacteria protects arthropods from host plant cyanide poisoning (2014) In: eLife, doi:10.7554/eLife.02365