Grant: Canada Research Chairs

In many biological systems, unrelated organisms have evolved interactions with each other so stable and integrated that they appear to function, to the casual human observer, as one. This phenomenon was discovered 150 years ago in lichens. Since this discovery, similar interactions, often called symbioses, have been discovered throughout the natural world, and are now understood to underlie the most consequential evolutionary innovations in earthly life, the evolution of mitochondria and chloroplasts. Symbiosis research focuses on which organisms are involved in such interactions; the trade of goods and/or services that underpins the interaction and which partner, if any, benefits; and how the interaction arises, persists and breaks down. The unique and as-yet unexplained ability of lichens to generate emergent three-dimensional architectures, as well as their ability to survive some of the most extreme conditions for life, has led them to be called the “holy grail of plant-microbe interactions”. Lichens are widely considered to consist of two partners, with a fungus receiving photosynthesis-derived algal sugar subsidies for its own growth. Recent work by Dr. Spribille has however questioned these paradigms. On account of Dr. Spribille's work, it is now well known that lichens usually harbour more than two stable partners, and the gene repertoires of their fungal symbionts are not consistent with those of a symbiont that uses sugar subsidies only for growth. What, then, are the partners doing with their traded goods? Dr. Spribille's research program focuses on using genomics to reveal what changed in symbiont genomes when their ancestors switched to living inside lichens. By mapping gene evolution behind cellular processes such as carbohydrate modification and production of defence compounds, it will provide the highest resolution picture to date of what happened in lichens at the level of component symbionts at key transition points, such as onset of received carbon subsidies, switches in sugar type, and switches of partner. Resolving lichen interactions will be a major contribution to understanding the role of symbiosis in generating complexity and enabling life in environmental extremes.