A novel mycorrhiza induced plant CLE peptide controls the root development and improves arbuscule lifespan
S. BASHYAL, H. EVERETT, S.E. MATSUURA, L.M. MÜLLER
Plant Molecular and Cellular Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037 School of Biological Sciences, University of California San Diego, La Jolla, CA 92093 Department of Biology, University of Miami, 1320 S Dixie Hwy, Coral Gables, FL 33146

CLAVATA3/EMBRYO SURROUNDING REGION-related (CLE) peptides are known to regulate multiple symbiotic processes. The role of CLE peptides during arbuscular mycorrhizal (AM) symbiosis, a mutualistic relationship between plants and AM fungi, are not thoroughly explored. AM fungi develop finely branched hyphal structures (arbuscules) inside plant root cortex cells, where nutrient exchange takes place. Here, we used Medicago truncatula to functionally elucidate the role of a novel mycorrhiza-induced CLE propeptide, mycCLE, in root development and fungal colonization. In a GUS reporter assay performed in AM-colonized roots, we identified the mycCLE promoter to be active in colonized cortical cells, lateral root primordia and root tip. Using a plate-based assay with synthetic mycCLE, we observed that the peptide inhibited the growth of primary root and lateral roots by affecting vasculature patterning, while leading to early branching of lateral roots. Constitutive overexpression and synthetic application of mycCLE led to the increase of root length colonization and arbuscule density in an inoculation experiment using the AM fungus Rhizophagus irregularis. Further, RNAseq analysis showed the downregulation of arbuscule senescence-related genes and suppression of the host jasmonic acid response. Thus, we hypothesize that mycCLE prolongs arbuscule lifespan that is directly related to the nutrient transport to plants.