Assistant Professor University of Miami Coral Gables, Florida
Body of Abstract: Most land plants form mutually beneficial interactions with soil borne Glomeromycotina fungi in a symbiosis called arbuscular mycorrhiza (AM). Fungal hyphae absorb micronutrients such as phosphate from the soil and provide them to the roots in exchange for carbon. The host plant controls the intensity of the symbiosis through a complex signaling network between colonized root cells and other tissues of the plant. We identified several genes encoding secreted peptides of the CLV3/ESR-related (CLE) family – members of which have previously been identified to act as nutrient or developmental signals in other plant systems – that are up-regulated during AM symbiosis in roots of the legume Medicago truncatula. We found that the AM-induced MtCLE53 acts as a negative autoregulatory signal restricting subsequent AM fungal root colonization by down-regulation of several key enzymes producing strigolactones – the cues emitted to the rhizosphere by nutrient-starved plants to attract beneficial symbionts.MtCLE53 is induced in the vascular tissue in the vicinity of root cortex cells colonized by AM fungi, and its function is dependent on the CLAVATA1-like leucine-rich repeat receptor-like kinase SUNN. Others reported that SUNN is also involved in the perception of MtCLE13, a peptide hormone closely related to MtCLE53, which is induced in M. truncatula roots in response to symbiosis with nitrogen-fixing rhizobia. Intriguingly, we found that ectopic over-expression of MtCLE13 did not influence AM symbiosis, indicating that despite high sequence similarity and involvement of the same receptor, there is considerable functional specificity among different members of the CLE family. Current research focuses on elucidating how SUNN distinguishes between various CLE signals to elicit a specific response. We hypothesize that SUNN is part of a receptor complex that integrates various signals of plant symbiosis and nutrient status to fine-tune symbiosis intensity and ensure an optimal cost-benefit balance for the host plant.