MYC and infection: While NFP on the one hand is required for Myc-LCO dependent activation of Ca2+ spiking [10] and for almost all pre-symbiotic transcriptional responses towards Myc-LCOs supplied at 10-7/-8 M [7], nfp-1 mutants on the other hand are not impaired in mycorrhization [49], indicating that at low concentrations, LCO signals are probably not essential for AM fungal entry and the infection of root cortical cells.