Abstract
Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that also establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi. Here, we show that many other fungi also produce LCOs. We tested 59 species representing most fungal phyla, and found that 53 species produce LCOs that can be detected by functional assays and/or by mass spectroscopy. LCO treatment affects spore germination, branching of hyphae, pseudohyphal growth, and transcription in non-symbiotic fungi from the Ascomycete and Basidiomycete phyla. Our findings suggest that LCO production is common among fungi, and LCOs may function as signals regulating fungal growth and development.
Highlights
Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi
These exudates were assayed for LCO activity using the highly sensitive root hair deformation response triggered by LCOs in barrel medic (Medicago truncatula) and common vetch (Vicia sativa)[1,2]
To test the specificity of the root hair branching response to LCOs, we examined the effect of short COs, polymers of four to five GlcNAc residues (CO4 and CO5), which are precursors of LCOs and have been shown to activate the CSSP11,12
Summary
Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi. Additional studies have shown that these two dissimilar symbioses share a highly conserved Common Symbiosis Signaling Pathway (CSSP), which is activated in plants by Nod- or Myc-LCOs to allow root colonization (either Nod or mycorrhization, respectively[5,6]) In both symbioses, LCOs are perceived at the plasma membrane by receptor-like kinases with extracellular LysM domains[7,8]. L. bicolor colonizes the roots of Populus, a host plant that contains the genetic components of the CSSP and can be colonized by AM fungi[9]; another EM fungus that was suspected to produce LCOs, Hebeloma cylindrosporum, colonizes mostly pine, which does not contain the components for the CSSP10 This latter finding suggests that LCOs may have functional roles beyond symbiotic signaling. We show that LCOs have regulatory functions in fungal development
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