Genomic and Chemical Evidence on Biosynthesis of Taxane Diterpenoids in Alternaria Isolates from Cupressaceae.

Alternaria species (Deuteromycetes, Ascomycota) as ubiquitous fungi and prolific producers of a variety of toxic compounds are a part of microbiomes of plants, humans, and animals, mainly causing disease, allergic reactions, and toxicosis. However, some species have also been reported as endophytic microorganisms with highly bioactive metabolites. Our previous results indicate that potentially endophytic Alternaria species from Cupressaceae produce bioactive metabolites that possibly contribute to plant holobiont's health. Here, a possible mechanism behind this bioactivity is elucidated. As some endophytic fungi are reported to produce cytotoxic taxane diterpenoids, eight potentially endophytic Alternaria isolates from our collection were analyzed for the presence of the key genes of the paclitaxel (Taxol) biosynthetic pathway, i.e., taxadin synthase (ts), 10-deacetylbaccatin III-10-O-acetyltransferase (dbat), and C-13-phenylpropanoid side-chain CoA acyltransferase (bapt). The presence of all genes, i.e., ts, dbat, and bapt, was detected by PCR in six isolates and dbat and bapt in two isolates. Chemical analyses of the fermentation broths by TLC and HPLC chromatography and IR spectroscopy indicated the synthesis of the final product, i.e., paclitaxel. So, we introduce the synthesis of taxane diterpenoids as a possible mechanism by which Alternaria occupies the plant niches and protects the plant holobiont in the presence of competing microorganisms.