DISSERTATION RESEARCH: Diversity and Functions of Interactions between the Liverwort Marchantia polymorpha and its Fungal Endophytes

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Plants are defining components of natural ecosystems where they provide habitats for other organisms and influence the composition of soils and the atmosphere. Fungi, though less conspicuous, significantly affect the success of living plants in addition to breaking down dead matter. Fungi that live inside healthy plants, called fungal endophytes (hereafter simply endophytes), can benefit plants in many ways, including promoting growth, enhancing disease resistance, and increasing resilience to extreme conditions such as drought. Therefore, understanding how endophytes interact with their host plants is critical for managing wild ecosystems as well as increasing productivity in forestry and agriculture as plants respond to extreme weather in a changing climate. Endophytes have been found in nearly all plants sampled to date but there are few direct studies of the mechanisms behind their functions. This project investigates the diversity and functions of endophytes in a liverwort. This project will sample the diversity of endophytes in a model liverwort, Marchantia polymorpha, and investigate what factors influence this diversity. M. polymorpha grows well in the laboratory, so this project will directly test the effects of individual endophytes. Using genetic methods, the researcher will identify possible mechanisms behind the observed interactions. In addition, the study system developed in this project will provide many future opportunities for plant-endophyte interaction research.The researchers will collect Marchantia polymorpha plants from ten populations across the USA and characterize the diversity of the liverworts and their endophytes. Liverwort genotypes will be assessed using Restriction-site Associated DNA sequencing (RAD-seq) to sample sites throughout the genome. Internal fungal diversity will be sampled by surface sterilizing whole M. polymorpha plants, extracting total DNA, then amplifying and sequencing a fungal barcoding gene region. The researchers will test for correlations between fungal community diversity and composition, host genotypes, and population locations. These data will provide an ecological context for previous experiments testing the effects of cultured endophytes on M. polymorpha in laboratory growth assays. To investigate the mechanisms behind the liverwort-endophyte interactions observed in the laboratory, the researchers will sequence the transcriptomes of the plant and selected fungi when grown alone and together. Four fungi will be used: a growth-enhancing fungus, a detrimental fungus, and close relatives of each which show a neutral interaction. Comparing the levels of gene expression between the treatments and controls will allow the researcher to form hypotheses about which cellular systems may be important in controlling the observed interactions.