Isolation, Characterization and Targeted Metabolic Evaluation of Endophytic Fungi Harbored in 14 Seed-Derived Hypericum Species.

Medicinal plants of the genus are rich sources of bioactive naphthodianthrones, which are unique in the plant kingdom, but quite common in fungal endophytes. Cultivable endophytic fungi were isolated from 14 different spp. originating from seeds grown under conditions and further acclimated to outdoor conditions. Among 37 fungal isolates yielded from the aerial and underground plant organs, 25 were identified at the species level by the fungal barcode marker internal transcribed spacer rDNA and protein-coding gene region of . Ten of them were isolated from spp. for the first time. The axenic cultures of the isolated endophytes were screened for the production of extracellular enzymes, as well as bioactive naphthodianthrones and their putative precursors by Bornträger's test and HPLC-HRMS. Traces of naphthodianthrones and their intermediates, emodin, emodin anthrone, skyrin, or pseudohypericin, were detected in the fungal mycelia of and isolated from and , respectively. Traces of emodin, hypericin, and pseudohypericin were released in the broth by , and during submerged fermentation. These endophytes were isolated from several hypericin-producing spp. Taken together, our results reveal the biosynthetic potential of cultivable endophytic fungi harbored in plants as well as evidence of the existence of remarkable plant-endophyte relationships in selected non-native ecological niches. A possible role of the extracellular enzymes in plant secondary metabolism is discussed.