Dissertation Research: Assembly, maintenance, and function of the plant-endophyte symbiosis

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Living within the leaves of every plant species on our planet are diverse communities of microscopic fungi, known as fungal endophytes. Unlike pathogens that cause plant disease, fungal endophytes can be beneficial for their plant hosts. Due to their variety of health benefits for plants, there is currently great interest in using endophytes in sustainable agriculture and biological control. Although recent research has begun characterizing endophyte communities and their functions in agricultural crops and other plants, we lack basic knowledge of how endophytes benefit the plants in which they live. Just as we understand the mechanisms by which drugs promote human health, understanding the mechanisms by which endophytes interact with plant physiology and the immune system is imperative for using these fungi in restoration ecology and sustainable agriculture. This research will work to uncover these mechanisms, improving knowledge of how and why plants and fungal endophytes form and maintain their beneficial relationships. Additionally, this research will train undergraduate students, as well as high school students.This research will use Theobroma cacao, the cacao tree, as a host species for studying assembly, maintenance, and function of the plant-endophyte interaction. First, the researchers will use total RNA sequencing to understand how changes in plant and fungal gene expression underlie increased plant pathogen resistance following application of leaf litter to conspecific seedlings. The researchers expect that exposure to leaf litter, a source of endophytic inoculum, will not only alter baseline gene expression in plants, but will also change how plants respond genetically to pathogen infection. Second, this project will use stable-isotope techniques to track the nutrient exchange between plants and endophytes, and determine if plants "pay" endophytes to mount an immune response against their enemies. The researchers hypothesize that plants can direct nutrients toward more beneficial endophytic fungi.