Evolution of resistance to plant defense compounds



Secondary metabolites (SMs) are critical mediators of the ecological interactions of plants that influence the richness and diversity of beneficial and pathogenic microbial communities in the phytobiome. Examples of widespread SMs include stilbenoids, a diverse group of aromatic compounds that defend plants against bacteria and fungi and also occur as enzyme-inhibiting byproducts of the degradation of lignins, which provide durability the plant cell wall. Metabolic adaptations to neutralize or degrade toxic host SMs, including stilbenoids, give fungi a fitness advantage on plant substrates, and are frequently associated with increased virulence. Unlike in most eukaryotes, fungal genomes often encode metabolic pathways in physical gene clusters that also include complementary regulatory and transport functions. A large number of diverse stilbene catabolism clusters (SCCs) were recently inferred through comparative genomics, and three of these were partially characterized for enzyme function in vitro. Many of these clusters appear to be self-contained modules encoding the complete breakdown of stilbenoids as a carbon source. The evolutionary mechanisms for the origin and persistence of these clusters may involve linkage of co-adapted genes during both vertical and horizontal gene inheritance, driven by physicochemical constraints on metabolism. Fungal gene clusters such as these may contribute to the evolvability of plant-associated fungi, facilitating metabolic diversification and pathogen emergence.

Funded by OARDC Research Enhancement Competitive Grants