The Effect of Mycorrhization with Fungi of Different Efficiency on the Root Metabolome of Medicago lupulina Within Development.

The mechanisms underlying the symbiotic efficiency of arbuscular mycorrhizal (AM) fungi are actively debated, but comparative metabolomic studies with fungi of contrasting efficiency are scarce. This study aimed to evaluate the influence of effective (Rhizophagus irregularis RCAM00320) and ineffective (Glomus sp. 129.1Te) AM fungal strains on the root metabolome of the responsive Medicago lupulina line MlS-1 at two vegetative and two reproductive stages. Using GC-MS, over 150 metabolites (amino acids, carboxylic and fatty acids, sugars, etc.) were annotated. Effective AM symbiosis was associated with increased levels of phosphoric acid, trehalose, and free fatty acids 16:1, as well as a decreased pool of tricarboxylic acid cycle intermediates (citrate, malate, succinate) and a reduction in γ-aminobutyric acid from the branching stage to fruiting. The comparison revealed that the branching initiation stage, characterized by low arbuscule abundance in ineffective treatment, is likely a main critical metabolic transition determining symbiosis efficiency. Novel metabolic markers of effective AM were identified. Network analysis revealed a divergence of amino acid and fatty acid clusters under effective mycorrhization, whereas under ineffective mycorrhization these clusters were less separated and closely linked in the control. Thus, inoculation with strains of contrasting efficiency generates distinct phenotypes, with effective AM inducing the most pronounced metabolome rearrangements in development.