Myristate as a carbon and energy source for the asymbiotic growth of the arbuscular mycorrhizal fungus Rhizophagus irregularis, bioRxiv, 2019-08-11

AbstractArbuscular mycorrhiza (AM) is one of the most widespread mutualistic symbioses, which is formed between the majority of land plants and soil-borne fungi belonging to Glomeromycotina. AM fungi are obligate symbionts that cannot complete their natural life cycle without a host. Recent evidence suggests that lipids synthesized by a host are transferred to AM fungi that possess no fatty acid synthase genes in their genome and that mutations in lipid biosynthesis-related genes of the host lead the symbiotic interaction to fail (1–3). We hypothesized that lipids derived from plants are crucial for AM fungal growth and reproduction. In this study, we evaluated whether AM fungi can grow on medium supplied with fatty acids under asymbiotic conditions without the host. Myristate led to an extensive hyphal growth of Rhizophagus irregularis and an increase in biomass production. Other examined fatty acids showed no effect on biomass production. Myristate also induced secondary spore formation. The myristate-induced spores can germinate, colonize carrot hairy roots, and form the next generation of mature daughter spores. A fluorescently labeled fatty acid probe was taken up by branched hyphae of AM fungi. Tracer experiments using 13C-labeled myristic acid showed that myristate and its metabolites were utilized for the synthesis of triacylglycerol and cell wall components of AM fungi. Furthermore, myristate activated ATP generation in the fungal hyphae. Here we demonstrate that myristate is utilized as a carbon and energy source for biomass production and sporulation under asymbiotic conditions.

biorxiv microbiology 0-100-users 2019

 

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