Several groups of LysM-RLKs are involved in symbiotic signal perception and arbuscular mycorrhiza establishment

Lipo-chitooligosaccharides (LCO) and short-chain chitooligosaccharides (CO) are produced by arbuscular mycorrhizal fungi (AMF) and activate the plant symbiosis signalling pathway, which is essential for mycorrhiza formation. High-affinity LCO receptors belonging to the LysM receptor-like kinase (LysM-RLK) phylogenetic group LYR-IA play a role in AM establishment, but it is unclear which proteins are the plant high-affinity short-chain CO receptors.

Here we studied members of the uncharacterized LYR-IB group, and found that they show high affinity for LCO, short- and long-chain CO, and play a complementary role with the LYR-IA receptors for AM establishment. While LYR-IB knock out mutants had a reduced AMF colonization in several species, constitutive/ectopic expression in wheat increased AMF colonization. LYR-IB function is conserved in all tested angiosperms, but in most japonica rice a deletion creates a frameshift in the gene, explaining differences in AM phenotypes between rice and other monocot single LYR-IA mutants.

In conclusion, we identified a class of LysM-RLK receptors in angiosperms with unique biochemical properties and a role in both LCO and CO perception for AM establishment.