Mini-symposium on Symbiosis – University of Copenhagen

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Mini-symposium on Symbiosis

On 15 Dec Associate Professor François Lutzoni from Duke University visits PLEN and gives a talk on “A multidimensional exploration of the lichen symbiosis within the macroevolutionary context of fungi and land plants”. Associate Professor Michael Thomas-Poulsen from Department of Biology and Professor Hans Thordal-Christensen from PLEN will also give talks at this mini-symposium.

Francois Lutzon15.00-15.50 François Lutzoni: A multidimensional exploration of the lichen symbiosis within the macroevolutionary context of fungi and land plants.

Interactions between photoautotrophs and fungi are ubiquitous in nature.  This is reflected by multiple successful types of symbioses (e.g., mycorrhizal, endophytic, and lichenic), associated with tremendous diversifications of fungal and plant species. Specificity (specialists versus generalists) and the transmission of symbionts to the next generation are important factors shaping these symbiotic interactions.  In addition to carbon fixation, nitrogen transport seems to have played a major role in enabling the establishment of these symbioses and accelerating the diversification rates of the Leotiomyceta and land plants.

LichensOur divergence time estimates of fungal and land plant evolution support multiple synchronous codiversifications, or unilateral diversifications of one partner in association with key innovations in the other partner, in concordance with strong codependence between plants and fungi. The evolution of these symbioses can be interconnected. For example, we discovered that the evolution of endophytic fungi found in land plants might have originated in the lichen microbiome.  Using next generation sequencing we also found that the lichen microbiome hosts highly diverse bacterial communities enriched in members of the Rhizobiales, some of which have been found only in lichens. 

Michael Thomas-Poulsen15.55-16.30 Michael Thomas-Poulsen: Integrating next-generation sequencing tools to elucidate complementary roles in an ancient symbiosis between farming termites, their fungal crops and co-adapted bacteria communities.

Approximately 30 MYA, the ancestors of the higher termite sub-family Macrotermitinae and the basidiomycete fungus Termitomyces joined forces in what was to become one of the most sophisticated plant biomass decomposition symbioses on Earth. At that time, the termites had already lost their Protist gut symbionts and replaced them with bacteria, but the degree to which the innovation of fungiculture induced a functional shift in the gut microbiota has remained unclear.

TermiteI will describe the core gut microbiota composition of the termite subfamily and offer the first metagenomic insight into the functional roles of these communities. Focusing on the carbohydrate-active enzymes coded for by Termitomyces and gut microbes in Macrotermes natalensis, I will show that gut bacteria primarily contribute enzymes for final digestion of simple polysaccharides after Termitomyces has degraded the more complex carbohydrates, and that gut microbes provide enzymes for decomposing fungal cell walls. The bacterial genera making these enzymes are consistently over-represented in fungus-growing termites relative to other higher termites that have a higher preponderance of cellulolytic bacteria. The shift in gut microbiota function after Termitomyces domestication thus appears to involve both complementary division of labor and targeted digestion of the novel food offered by Termitomyces.  

Hans Thordal-Christensen16.30-17.05 Hans Thordal-Christensen: Host membrane processes in a plant-pathogen symbiosis.

Symbiosis is generally thought to be mutually beneficial. However, this does not have to be the case. You can have symbioses that are only beneficial for one of the partners. This is for instance the case in many host-pathogen interactions, where only the pathogen enjoys it, while the host suffers, but does not die. These symbioses can reach a very high level of intimacy, where the pathogen lives inside a niche in the host cells. Many bacterial pathogens are using this strategy in animal and human cells. They are initially engulfed by the host cell, but rapidly transfer effectors to the host cell to influence the membrane trafficking pathway and prevent degradation in the lysosome. This allows the bacteria to thrive in a membrane niche inside the host cell.

MildewWe are studying a similar host-pathogen interaction between plants and powdery mildew fungi. In this case, the fungal pathogen lives partly outside, partly inside the host cell. Here a specialised fungal structure, a haustorium, is formed in a niche delimited by a poorly understood extra-haustorial membrane. Since the haustorium can live inside the living host cell for more than a week, we consider this a symbiosis. We are studying the host membrane trafficking processes related to the invasion, and have made observations that the extra-haustorial membrane shares properties with the host ER membrane.

17.05 – 18.00   Networking with wine, beer, soft drinks and snacks.