Genome Organization and Transmission Genetics of Arbuscular Mycorrhizal Fungi

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The goal of this project is to uncover genome organization (size and ploidy) and the reproductive mode of arbuscular mycorrhizal fungi (AM fungi, Glomeromycota) using genetic, population genetic and cytological approaches. AM fungi colonize roots of most land plants, including many crop species, where they facilitate uptake of minerals from the soil. Consequently, they are a key component of terrestrial ecosystems. Yet, AM fungi remain one of the least genetically understood microorganisms. With no sexual morphology, AM fungi are hypothesized to reproduce clonally, but there are theoretical and empirical reasons to doubt this hypothesis. To select tools needed to challenge the hypothesis of clonality, a thorough analysis of genome organization will be performed. Next, patterns of genetic variation in a field population of an AM fungus will be analyzed to detect signatures of recombination or clonality. This work will be supplemented by a cytological study tracing the fate of nuclei during AM fungal life cycle, for which genetically transformed strains expressing GFP-labeled histone will be constructed to enable visualization of nuclei in living cells. Understanding the genome organization of AM fungi is essential for future sequencing of AM fungal genomes. Reproductive mode is a single most important piece of information needed to develop transmission genetics of AM fungi, which will be greatly aided by the genetic transformation system developed in this study. Another product of this work, genetic markers, will augment the phenotype-based taxonomy of AM fungi. All these tools will enable systematic evaluation of the role of AM fungi in nature and agrosystems, and facilitate breeding (if reproduction is sexual) or selection (if reproduction is clonal) of AM fungi for specific purposes of improved plant mineral nutrition, pest control, protection from drought, salinity, or toxic metal stress. Glomeromycota, if proven clonal, may represent an ancient asexual lineage and they may offer a system to study mechanisms of long-term evolutionary survival in the absence of meiotic recombination.