Lipo-chitooligosaccharides: from plant symbiosis to conserved fungal signals

Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by fungi that also establish symbiotic relationships with plants, notably the arbuscular and ecto-mycorrhizal fungi. Here, we investigated whether other fungi also produce LCOs. Of the 59 species tested, representing most phyla of the Kingdom Fungi, we found that 53 produce LCOs that can be detected by functional assays and/or by mass spectroscopy. LCO treatment of representative species of non-symbiotic fungi from the Ascomycete and Basidiomycete phyla affected spore germination, branching of hyphae, pseudohyphal growth, and transcription. These findings suggest that LCOs are common to many fungi and likely function as regulatory signals of fungal growth and development.