Fungal Endophytes as Efficient Sources of Plant-Derived Bioactive Compounds and Their Prospective Applications in Natural Product Drug Discovery: Insights, Avenues, and Challenges

Fungal endophytes are well-established sources of biologically active natural compounds with many producing pharmacologically valuable specific plant-derived products. This review details typical plant-derived medicinal compounds of several classes, including alkaloids, coumarins, flavonoids, glycosides, lignans, phenylpropanoids, quinones, saponins, terpenoids, and xanthones that are produced by endophytic fungi. This review covers the studies carried out since the first report of taxol biosynthesis by endophytic Taxomyces andreanae in 1993 up to mid-2020. The article also highlights the prospects of endophyte-dependent biosynthesis of such plant-derived pharmacologically active compounds and the bottlenecks in the commercialization of this novel approach in the area of drug discovery. After recent updates in the field of ‘omics’ and ‘one strain many compounds’ (OSMAC) approach, fungal endophytes have emerged as strong unconventional source of such prized products.

Microscopy of Taxomyces andreanae, a new taxon isolated from Taxus

A newly described fungus, Taxomyces andreanae Strobel, Stierle, & Hess. has also been isolated from (Taxus brevifolia Nutt.), The growth pattern of the fungus was determined by growing it on various plant species, plant parts and agar cultures. The morphological characteristics appeared to be more diverse when the fungus was grown on twigs of yew wood. Therefore, the purpose of these investigations was to use electron microscopy to more carefully observe the nature of fungal growth and bulbil formation of T. andreanae on twigs of yew wood.Small pieces of sterile plant tissues were used to grow the fungus. For microscopy studies, procedures outlined by Upadhyay et al. were used, which consisted of fixation and dehydration followed by critical point drying and sputter coating for SEM, and embedment in Spurr resin for TEM. All SEM photos were taken at 10 kV. Fungal colonies had sparse to very dense concentrations of hyphal cells (Fig. 1) which, in some areas of cultures, produced hyphal cells which averaged from 1.25 μm to larger cells which averaged 3.75 μm in diameter.