The Plant Growth-Promoting Fungus MF23 ( sp.) Increases Production of (Orchidaceae) by Affecting Nitrogen Uptake and Assimilation.

Kimura et Migo is a traditional and scarce medicinal orchid in China. Mycorrhizal fungi could supply nitrogen (N) to orchids for seed germination and seedling recruitment. However, the N transport mechanism between orchids and the fungus is poorly understand. Early studies found that the fungus MF23 ( sp.) could promote the growth of . To better dissect the molecular interactions involved in N transport between and MF23, transcriptome and metabolome analyses were conducted on conventional and mycorrhizal cultivations of . Moreover, validation tests were carried out in the greenhouse to measure net fluxes of and of roots by a non-invasive micro-test technology (NMT), determine N assimilation enzyme activity by the ELISA, and analyze the expression level of differentially expressed genes (DEGs) of N transporters and DEGs involved in N metabolism by RT-qPCR. Combined transcriptome and metabolome analyses showed that MF23 may influence N metabolism in . The expression of (nitrate transporter-activating protein), (ammonium transporter), (amino acid transporters), (oligopeptide transporters), and (glutamate dehydrogenases) in symbiotic was upregulated. NMT results showed a preference for in and indicated that MF23 could promote the uptake of and , especially for . ELISA results showed that MF23 could increase the activity of glutamine synthetase (GS) and glutamate dehydrogenase. This study suggested that MF23 increases the production of by affecting N uptake and assimilation capacity.