Evaluation of fungal diversity in the rhizosphere of Alkanna tinctoria and impact of selected fungi on growth and production of secondary metabolites in Alkanna tinctoria and Echium vulgare by Yanyan Zhao

Plants roots are associated with very diverse microbial communities among which endophytic bacteria and fungi and arbuscular mycorrhizal fungi (AMF). These microorganisms play key roles in plant health, development and productivity and may as well influence plant metabolome, thus impacting the production of secondary metabolites (SMs).

Alkanna tinctoria L. and Echium vulgare are plant species belonging to the Boraginaceae family, with well-known medicinal virtues. Their roots are rich in naphthoquinones, especially alkannin, shikonin (A/S) and their derivatives (A/Sd), whose pharmaceutical uses are widely documented. However, if and how microorganisms associated to the roots of these plants influence the production of SMs (e.g. A/Sd) are practically unknown. In this perspective, the present thesis investigated the fungal community associated with the roots of A. tinctoria during the different stages of plant development. In parallel, AMF from GINCO and fungal endophytes and AMF isolated from the roots of A. tinctoria grown in the wild in Greece were tested on growth and A/Sd production of A. tinctoria and E. vulgare. The experiments were conducted in pots or with hairy roots in vitro and A/Sd analysed by High-Performance Liquid Chromatography coupled with Photodiode Array detection (HPLC-PDA) and HPLC coupled with High-Resolution Mass Spectrometry detection (HPLC-HRMS/MS).

In conclusion, these studies indicate the importance of applying endophytic fungi and AMF in the production of SMs in medicinal plants. Further studies are needed to investigate the mechanisms involved in the production of SMs, especially A/Sd in plants associated to specific endophytic fungi /AMF and on the cultivation conditions needed for optimal production.