CORYNE modulates Medicago truncatula inflorescence meristem branching and plays a conserved role in the regulation of arbuscular mycorrhizal symbiosis.

The CLAVATA signaling pathway regulates plant development and plant-environment interactions. CLAVATA signaling consists of mobile, cell-type or environment-specific CLAVATA3/ESR-related (CLE) peptides, which are perceived by a receptor complex consisting of leucine-rich repeat receptor-like kinases such as CLAVATA1 and receptor-like proteins such as CLAVATA2, which often functions with the pseudokinase CORYNE (CRN). CLAVATA signaling has been extensively studied in various plant species for its developmental role in meristem maintenance. In addition, CLAVATA signaling was implicated in plant-microbe interactions, including root nodule symbiosis and plant interactions with mutualistic arbuscular mycorrhizal (AM) fungi. However, knowledge on AM symbiosis regulation by CLAVATA signaling is limited. Here, we report a dual role for Medicago truncatula CRN in development and plant-microbe interactions. In shoots, MtCRN modulates inflorescence meristem branching. In roots, the MtCRN promoter is active in vascular tissues and meristematic regions. In addition, MtCRN expression is activated in cortex cells colonized by AM fungi and negatively regulates root interactions with these microbes in a nitrogen-dependent manner; negative AM symbiosis regulation by CRN was also observed in the monocot Zea mays, suggesting this function is conserved across plant clades. We further report that MtCRN functions partially independently of the AM autoregulation signal MtCLE53. Transcriptomic data revealed that M. truncatula crn roots display signs of perturbed nutrient, symbiosis, and stress signaling, suggesting that MtCRN plays various roles in plant development and interactions with the environment.