Decoding Mycangia: Gene expression at the interfaces of two beetle-fungus symbioses

Bark and ambrosia beetles are often discussed in the context of their highly publicized impacts on forest health, some of which are facilitated through the nutritional symbioses certain groups have developed with wood-colonizing fungi. In the most specialized of these relationships, beetles ensure transfer of a particular species from tree to tree through specialized organs called mycangia. However, what a mycangium “does” on a molecular level to ensure transport and selection of some fungi over others remains unclear. With the aid of existing and newly generated genomic assemblies for various bark and ambrosia beetles and their symbionts, we are harnessing RNAseq of insects, fungi, and mycangia to perform differential gene expression analysis, with the goal of identifying effectors on both sides of the symbiosis that play a potentially significant role in facilitating fungal transport and selection. We focus on two, independently evolved beetle-fungus mutualisms: Dendroctonus frontalis and its two symbionts Entomocorticium and Ceratocystiopsis, as well as Xylosandrus crassiusculus and its symbiont Ambrosiella roeperi. By examining patterns within both symbioses, which represent different beetle and fungal lineages, lifestyles, and mycangial locations, we infer candidate genes for future functional experiments. Ultimately, we document patterns of convergence that can be validated and elaborated upon in other bark/ambrosia beetle systems.