DISSERTATION RESEARCH: Does hosting arbuscular mycorrhizal fungi in modular structures facilitate discrimination against cheaters?

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The majority of terrestrial plant species depend on symbiotic fungi that live inside their roots ("mycorrhizal fungi") to both meet their mineral nutrient demands and increase their defenses against pests and disease. However, many strains of fast-growing mycorrhizal fungi have evolved to exploit their hosts without providing any of these services, leaving plants with stunted growth and increased susceptibility to environmental stress. Brian Steidinger and James Bever of Indiana University (IU) seek to identify how plants can defend themselves against "cheater" fungi. The researchers enhance the impact of their scientific work through their involvement in public and minority outreach programs. Steidinger will integrate under-represented minorities in the sciences into his work at IU through the James Holland Summer Research Initiative (SRI). The SRI program brings both high school and freshmen college students to IU to participate in independent research. Steidinger will train SRI students how to measure mycorrhizal fungi and identify fungal cheaters, providing them with hands-on experience working in a lab setting. Further, Steidinger will recruit IU undergraduates to assist with the experimental and data analysis portions of the proposed research, helping them build skills they can apply towards independent thesis work. This research will enhance ongoing research by this team by providing a means to directly test model predictions using molecular techniques, measure the impact of AMF on plant nutrition, and expand an ongoing experiment to compare podocarps to plants that do not form nodulated roots. In addition, the researchers will test model predictions in a comparative study of AMF composition in a New Zealand podocarp forest. To achieve this, they created a theoretical model that identified features of a host plant that should increase their ability to spatially segregate and terminate resource investment into cheater strains. Second, they developed an experimental system of beneficial and cheater fungi to determine the effectiveness of defenses in different plant hosts. Finally, they collected roots from a forest system in order to determine if the defenses in their experimental system are effective against cheater fungi in the field. Steidinger and Bever hope to discover not only how plants defend themselves against exploitative fungi, but to shed light on common features of plant defenses that are likely to be applicable to a variety of mutualisms.