Program Book - 27th Fungal Genetics Conference

PLENARY SESSION ABSTRACTSSaturday, March 16 8:30 AM–12:00 NOONMerrill Hall and ChapelPlenary Session IV: Functional Ecology and Fungal CommunitiesChair: Jim AndersonMechanisms allowing the formation of new fungal pathogenic species on novel hosts, causing emerging diseases. Tatiana Giraud. ESE, Univ Paris 11,Orsay, France.We have studied different mechanisms allowing the formation of novel fungal pathogenic species on novel hosts. A theoretical model combined with aliterature survey have confirmed that mating within hosts in pathogenic ascomycetes may allow the rapid formation of new species by host adaptationalone, without requiring the evolution of mate choice. We also present studies on mechanisms of speciation in Microbotryum a fungal complex causingthe sterilizing anther-smut disease in many species of Caryophyllaceae. Multiple gene phylogenies and measures of hybrid inviability and sterility haverevealed the existence of multiple cryptic species, each being specific to one or a few plant host. We investigated the evolution of reproductive isolation inthe species complex, and showed that hybrid inviability and sterility increased with the genetic distance between the species. We show that selfing is themain barrier to gene flow between close species and that hybrid sterility arise because of karyotypic rearrangements. Cophylogeny analyses showed thatMicrobotryum species have evolved through frequent host shifts to moderately distant hosts. Current geographic distribution of host species seemed tobe of little relevance for understanding the putative historical host shifts, because most fungal clades had overlapping ranges. We did detect someecological similarities between host species that were diseased by closely related anther smut species, including pollinator or habitat similarities. However,genetics underlying the host-parasite interactions appeared to be the most important factor influencing host-shifts and specialization: multi-host speciesparasitized closely related plant species and related species in the Microbotryum phylogeny were associated with members of the same host clade. Weperformed a cross-inoculation experiment and showed that both host and pathogen phylogenies were indeed significant predictors of host range, with atleast partly independent effects. We investigated whether some Microbotryum species have arisen via hybridization.We also detected hybrids in natureand underwent a population genomic study to unravel the genomic architecture of introgression. Anther smut fungi appear as excellent models to unravelthe mechanisms of formation of new fungal species onto novel hosts.The decisive role of mycorrhizal fungi as regulators of carbon sequestration in boreal forest ecosystems. B.D. Lindahl, K.E. Clemmensen, I.T.M. Bödeker,E. Sterkenburg. Dept. Forest Mycol. & Path., SLU, Uppsala, Sweden.Boreal forest soils represent a significant global sink for carbon, but poor knowledge about the mechanisms that regulate the dynamics of soil carbonpools hampers the development of predictive ecosystem models. Such models are urgently needed to guide proper management of forest land, in orderto mitigate increasing atmospheric CO2 levels. By analysing the natural abundance of rare isotopes ( 14 C, 13 C and 15 N), we found that the mycelium ofmycorrhizal fungi represents a major source of soil carbon. Up to 50-70% of stored carbon was estimated to enter the soil via plant roots. Ratios betweenfungal biochemical markers (ergosterol and chitin) indicate that a rapid turnover of fungal mycelium minimizes carbon storage and favours efficientnitrogen recycling, whereas slow mycelial turnover favours carbon sequestration and immobilisation of nitrogen. In order to relate taxonomic andfunctional diversity to carbon dynamics, we used 454-sequencing of ITS2 amplicons to analyse fungal communities in environmental samples. In forestsoils with low nitrogen availability we found high abundance of ectomycorrhizal genera with differentiated extra-radical mycelium (cord formers). Memberof this group also correlated with high activities of classII peroxidases, known to facilitate break down of complex organic matter. Further evidence thatthese fungi act as “mycorrhizal white rotters” were obtained by amplification of peroxidase mRNA from soil extracts. The mRNA could be connected tomycorrhizal species by sequence homology. We propose that conditions of low nutrient availability favour the establishment of mycorrhizal species thatare adapted to minimize immobilisation of nitrogen in stable organic pools. As their own mycelium represents a major sink for soil-derived nutrients, thesespecies have to re-cycle their own biomass rapidly, in order to enable efficient delivery of nutrients to their host plants. They also possess potent oxidativeenzymes that may be used to increase mobility of organic nutrients. As a side-effect of their highly efficient nutrient recycling, presence of these fungi alsominimizes long term carbon sequestration in soils.Population Genomics of Saccharomyces Yeasts: Ecology and Adaptation. Edward J. Louis. Ctr Genetics and Genomics, Univ Nottingham, Nottingham,United Kingdom.The budding yeast, Saccharomyces cerevisiae, along with its close relatives, have only recently become reasonable models for the study of populationgenetics and evolution. This has been due to the lack of understanding of their natural history and ecology. Now that some understanding of budding yeastin nature is in hand, we can apply the powerful genetic and molecular tools available to questions of evolution through adaptation to ecological niches.The combination of population genomics and quantitative trait analysis has led to some understanding of the genetic architecture underlying traits whichmay be relevant to adaptation to particular environments in different yeast populations/species.27th Fungal Genetics Conference | 27