RUI: Confirmation of the roles of fungal genes in plant stress tolerance

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The 3-way symbiosis at the focus of this project is intriguing by virtue of the host plants gaining tolerance to soil temperatures of up to 125°F, a temperature at which most plants cannot grow. Plants survive this temperature due to their association with a particular fungus infected with a specific virus. Virally infected fungi living symbiotically with a host plant provide heat tolerance to a wide range of crop plants including tomato, corn, and rice. In a field trial, tomato plants harboring a fungal-viral symbiont showed improved growth and fruit production at elevated temperatures compared to non-infected plants. With the US economy losing more than $15 billion annually in crop production due to environmental factors, it will be potentially helpful to understand the mechanisms by which thermotolerance is induced in this virus-fugus-plant symbiosis. Insights gained from the research are likely to help in the development of methods to retain crop productivity in the face of high temperature stress. The project will provide hands-on multidisciplinary research training and educational opportunities for underrepresented minorities and first-generation college students at the University of West Alabama, a designated Minority Serving Institution. In addition, the project will include an educational outreach program for underprivileged K-12 students and adults through the Science Saturdays and Science Coffee Shop outreach programs, respectively. Finally, the physiological and molecular roles of fungal metabolites in stress tolerance will be of broad interest to the scientific community.In the geothermal soils of Yellowstone National Park, where temperatures can reach 65°C, a 3-way mutualistic association has evolved among panic grass (Dichanthelium lanuginosum) and a fungal endophyte (Curvularia protuberata) bearing a mycovirus, Curvularia thermotolerance virus (CThTV), which allows the 3 organisms to cooperatively survive extreme temperatures. Metabolic analyses showed significant changes during stress in our model system tomato (Solanum lycopersicum) infected with C. protuberata. The data collected in those analyses provide strong evidence that fungal trehalose and melanin are essential for the heat-stress tolerance mechanisms conferred by the 3-way symbiosis. In addition, CThTV contributes to thermotolerance via its interaction with a fungal translationally controlled tumor protein (TCTP) and catalase/peroxidase (KatG), which control fungal cell cycle and cellular redox, respectively. The hypotheses of this research are that C. protuberata carrying CThTV confers thermotolerance in plants via: 1) production of large quantities of trehalose, which is transported into plant tissues and functions as a signalling or osmoprotectant molecule to regulate plant biochemical processes during stress; 2) fungal melanin, which likely alters fungal cell walls to control trehalose transport into and accumulation in plant tissues during stress; and 3) CThTV, promotes thermotolerance by interacting with fungal TCTP and KatG to control fungal cell cycle and cellular redox during stress. In particular, the proposed research is designed to test the involvement of fungal trehalose, melanin, TCTP, and KatG genes in thermotolerant tomato associated with fungal-viral symbionts. The aims of this study are to: 1) knock down the trehalose, melanin, TCTP, and KatG genes in thermotolerant C. protuberata-carrying CThTV, thermotolerance will be completely abolished in trehalose or melanin synthesis knock downs, and reduced by knocking down TCTP or KatG expression; and 2) overexpress the same genes in non-thermotolerant C. protuberata without CThTV, plants are expected to gain thermotolerance characteristics in the case of trehalose and melanin biosynthetic gene overexpression, and exhibit improved thermotolerance in the case of TCTP and KatG overexpression.