Abstract

Receptor-like kinases (RLKs) are key cell signaling components. The rice ARBUSCULAR RECEPTOR-LIKE KINASE 1 (OsARK1) regulates the arbuscular mycorrhizal (AM) association postarbuscule devel-opment and belongs to an undefined subfamily of RLKs. Our phy-logenetic analysis revealed that ARK1 has an ancient paralogue in spermatophytes, ARK2. Single ark2 and ark1/ark2 double mu-tants in rice showed a nonredundant AM symbiotic function for OsARK2. Global transcriptomics identified a set of genes coregu-lated by the two RLKs, suggesting that OsARK1 and OsARK2 or-chestrate symbiosis in a common pathway. ARK lineage proteins harbor a newly identified SPARK domain in their extracellular re-gions, which underwent parallel losses in ARK1 and ARK2 in monocots. This protein domain has ancient origins in streptophyte algae and defines additional overlooked groups of putative cell surface receptors.