P-394 - A plant CLE peptide and its fungal mimic promote arbuscular mycorrhizal symbiosis via CRN-mediated ROS suppression

Many vascular land plants form a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi, which facilitate nutrient exchange in return for host-provided carbon via arbuscules, highly branched hyphal structures in root cortical cells. Plants tightly regulate AM symbiosis, while AM fungi can manipulate host signaling to regulate colonization. CLAVATA signaling, involving small, secreted CLE peptides and their receptors, emerged as a key pathway in plant-microbe interactions, including AM. Notably, all studied plant CLE peptides act as negative regulators of symbiosis. Here, we identify Medicago truncatula CLE16 (MtCLE16) as the first CLE peptide that positively regulates AM symbiosis. MtCLE16 is expressed in colonized root cells and its overexpression in the colonized cortex increases arbuscule abundance and length by fine-tuning their growth and lifespan. Functional and transcriptomic analyses reveal that MtCLE16 signals via the pseudokinase MtCRN and suppresses reactive oxygen species (ROS) accumulation, thereby promoting fungal colonization. Interestingly, AM fungi also encode CLE-like peptides similar to MtCLE16. Our data show that RiCLE1, a MtCLE16-like peptide from Rhizophagus irregularis also enhances AM colonization via MtCRN and ROS suppression, suggesting AM fungi exploit CLE mimicry to manipulate host signaling. Together, our findings reveal host and fungal CLEs promote AM symbiosis highlighting cross-kingdom mimicry as a fungal strategy to enhance colonization.