Effector that participates in the arbuscule development step of the symbiosis. Arbuscular mycorrhizal (AM) symbiosis is one of the most prominent and beneficial plant-microbe interactions that facilitates mineral nutrition and confers tolerance to biotic and abiotic stresses (PubMed:30233541). Is not involved in cell death processes (PubMed:30233541). Homodimer. Localizes to host nuclear bodies. Expressed during symbiosis establishment in parallel to host M.truncatula PT4, the gene coding for an arbuscule-specific phosphate transporter. The CRN proteins have modular architectures that include a signal peptide, a conserved N-terminus, and highly diverse C-terminal domains. The conserved CRN N-terminus harbors a distinct LXLFLAK motif, which is followed by the conserved DWL domain. A highly conserved HVLVXXP motif marks the end of the CRN N-terminal domains and forms a junction where diverse C-terminal domains are fused. Leads to an impairment of the symbiosis in M.truncatula and to a reduction of host PT4. Belongs to the Crinkler effector family.