Abstract
Medicinal plants of the genus Hypericum 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 Hypericum spp. originating from seeds grown under in vitro 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 tef1α. Ten of them were isolated from Hypericum 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 Bornträgerʼs test and HPLC-HRMS. Traces of naphthodianthrones
and their intermediates, emodin, emodin anthrone, skyrin, or pseudohypericin,
were detected in the fungal mycelia of Acremonium sclerotigenum and Plectosphaerella cucumerina isolated from Hypericum perforatum and Hypericum maculatum, respectively. Traces of emodin, hypericin, and pseudohypericin were released in
the broth by Scedosporium apiospermum, P. cucumerina, and Fusarium oxysporum during submerged fermentation. These endophytes were isolated from several hypericin-producing
Hypericum spp. Taken together, our results reveal the biosynthetic potential of cultivable
endophytic fungi harbored in Hypericum 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.
Key words
Hypericum spp. - Hypericaceae - endophytic fungi - Bornträgerʼs test - HPLC-HRMS - anthraquinones
- naphthodianthrones