Undergraduate Research Assistant University of Miami Miami Beach, Florida
Body of Abstract: Arbuscular mycorrhiza (AM) is an ancient mutualistic symbiosis between Glomeromycotina fungi and host plants. In this relationship, the fungus colonizes the plant root cortex cells to form branched hyphae called arbuscules which assist the host plant with water and nutrient uptake, particularly phosphate. Unable to produce carbohydrates, the fungus is provided with carbon from the host plant in the form of sugars and lipids. We previously described a negative regulatory pathway involving a root-derived peptide hormone (CLE53) which acts with the leucine-rich repeat receptor-like kinase SUNN to restrict symbiosis. As a consequence, sunn mutants display higher fungal colonization relative to the wildtype. Other proteins involved in regulating this symbiosis pathway have not been identified. Here we use Medicago truncatula to demonstrate that mutants in the membrane-associated kinase CORYNE are also impaired in symbiosis regulation. Because sunn and coryne mutants display similar phenotypes, we hypothesize CORYNE may act in concert with the CLE53-SUNN module, which fine-tunes AM by downregulating plant strigolactone production once a certain root colonization threshold is attained. We topically applied CLE53 to the plant roots and used genetic approaches to test this hypothesis. Further, we performed growth response assays to determine the physiological impacts of uncontrolled super-colonization. Whether these impacts result in over-sequestration of carbon by the microbial symbiont (parasitism) or provide increased benefit to the plant will be examined. Understanding these topics will allow us to maximally exploit this mutualistic symbiosis for the creation of “supermycorrhizal” mutants, reducing the need and use of unsustainable, finite chemical fertilizers. This ultimately will secure a more sustainable and stable crop food supply.