CLE signaling in arbuscular mycorrhiza symbiosis

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A large majority of plant species, including agronomically important crops such as rice, wheat and soy bean, rely on mutually beneficial interactions with soil-borne fungi in a symbiosis called arbuscular mycorrhiza (AM). Here, the plant benefits from the vast network of the fungal hyphae, which absorb micronutrients from the soil and transport them to the plant roots. The fungus in turn receives photosynthesis products from the plant and nutrient exchange occurs in specialized, highly branched fungal structures (arbuscules) within the root cortical cells. The establishment and maintenance of AM must be tightly regulated to guarantee an optimal cost-benefit balance in terms of nutrient release and uptake, a process which is largely controlled by the host plant and requires intercellular signaling between colonized root cells and other, non-colonized cells of the plant. A number of genes encoding small, secreted CLV3/ESR-related (CLE) peptides have been identified to be up-regulated upon fungal colonization in the grass model system Brachypodium distachyon as well as in the legume Medicago truncatula. In other systems, CLEs have been described as means of intercellular communication regulating mostly developmental processes, but also plant interaction with rhizobacteria and nematodes. Thus, the CLE peptides identified here could be excellent candidates for either short- or long-range intercellular signals regulating AM symbiosis, but so far their role remains elusive. Preliminary analyses in M. truncatula revealed that overexpression of MtCLE30 influences arbuscule development and promotes arbuscule degeneration, suggesting that plant control over fungal colonization could be regulated via CLE peptide signaling. In this project, we propose to characterize the role of CLE peptides during the formation and maintenance of AM symbiosis in monocots (B. distachyon) as well as in dicotyledonous legumes (M. truncatula). Both species serve as model systems for crop species and in a world where non-renewable fertilizer resources are dramatically declining, improvements in the sustainability of food production will increasingly rely on AM symbiosis.