The Root-Colonizing Endophyte Supports Nitrogen-Starved Seedlings with Nitrogen Metabolites.

The root-colonizing endophytic fungus promotes the root and shoot growth of its host plants. We show that the growth promotion of leaves is abolished when the seedlings are grown on media with nitrogen (N) limitation. The fungus neither stimulated the total N content nor did it promote NO uptake from agar plates to the leaves of the host under N-sufficient or N-limiting conditions. However, when the roots were co-cultivated with N-labelled , more labels were detected in the leaves of N-starved host plants but not in plants supplied with sufficient N. Amino acid and primary metabolite profiles, as well as the expression analyses of N metabolite transporter genes suggest that the fungus alleviates the adaptation of its host from the N limitation condition. alters the expression of transporter genes, which participate in the relocation of NO, NH and N metabolites from the roots to the leaves under N limitation. We propose that participates in the plant's metabolomic adaptation against N limitation by delivering reduced N metabolites to the host, thus alleviating metabolic N starvation responses and reprogramming the expression of N metabolism-related genes.