Recombine and succeed: a story of Cry toxins to expand the host range

Abstract

BackgroundCry toxins are the most widely used sources of bioinsecticides in agriculture; therefore, improving their functionality requires a deep understanding of natural evolution. It is thought that Cry toxins emerge via domain III swapping, yet the underlying mechanism remains unclear.ResultsWe detected 50 recombination events using a dataset of 368 clusters representing a known diversity of Cry toxins using a computational analysis. Not only do domain swaps engage all the domains, but they also occur continuously with approximately 70% of toxins participating in domain exchanges. Once they happen, hybrid toxins face purifying selection pressure reflecting the advantageous nature of receiving novel domains. When these domain exchanges occur, their host specificity changes dramatically. Strains housing these loci are enriched withcrygenes and can kill a broader spectrum of hosts, thus implying that recombination allows them to occupy novel niches. The respective recombination-affectedcrygenes are flanked with insertions and harbor highly conservative blocks between the domains’ borders suggesting that the genomic context governs the intra-domain recombination.ConclusionsOur study expands the established views of the role of recombination in the emergence of Cry toxins. Here, we demonstrate that the domain exchanges shape both Cry sequences, the composition of toxins in bacterial strains, and the sets of hosts affected. The collected data allowed us to propose a mechanism for how these toxins originate. Overall, the results suggest that domain exchanges have a profound impact on Cry toxins being a major evolutionary driver.