Short chain chito-oligosaccharides promote arbuscular mycorrhizal colonization in Medicago truncatula

During the establishment of arbuscular mycorrhizal (AM) symbiosis, the fungus and the host plant exchange chemical signals that are crucial to reciprocal recognition. Short-chain chitin oligomers (CO) released by AM fungi are known to trigger symbiotic signaling in all host plant species tested. Here we applied exogenous CO, derived from crustacean exoskeleton, to pot-grown Medicago truncatula inoculated with the AM fungus Funneliformis mosseae and investigated root colonization, plant gene regulation and biomass production. CO treatment strongly promoted AM colonization with significant increases in arbuscule development, biomass production and photosynthetic surface compared to untreated mycorrhizal plants. Gene expression analyses indicated that CO treatment anticipated the expression of MtBCP and MtPT4 plant symbiotic markers, during the first two weeks post inoculation. Altogether, our results provide evidence that plant treatment with symbiotic fungal elicitors, anticipated and enhanced AM development, encouraging the use of CO to promote AM establishment in sustainable agricultural practices.