Endophyte fungal diversity in Nothapodytes nimmoniana along its distributional gradient in the Western Ghats, India: are camptothecine (anticancer alkaloid) producing endophytes restricted to specific clades?

摘要

Nothapodytes nimmoniana Graham (Icacinaceae) is a small tree distributed along a 1600 km mountain range in the Western Ghats biodiversity hotspot in southern India. The stem wood of N. nimmoniana accumulates high concentration (about 0.3% by dry weight) of the anti-cancer alkaloid, camptothecine (CPT). Several endophytic fungi isolated from this plant have been shown to produce camptothecine in vitro. In this study, we examined the diversity and distribution of fungal endophytes of N. nimmoniana along its entire distributional range in the Western Ghats and investigated if the CPT-producing endophytes are restricted to any specific clade. The leaf and stem of N. nimmoniana were sampled from 18 sites along the Western Ghats span-ning 8-18 degrees N lat. Endophytes were recovered from all sites with the colonization frequency ranging from 0% to 52% across the sites. One hundred and four endophytic fungal isolates were recovered from 118 plants and characterized both morphologically and by sequencing the internally transcribed spacer region of the nuclear rDNA gene. The fungal isolates belonged to 45 species (44 Ascomycetes and one Basidiomycetes). Fusarium and Hypoxylon were the most predominant genera comprising over half of the total isolates. Interestingly, CPT-producing endophytes were not restricted to any specific clade. We discuss these results in the context of the growing interest in endophytic fungi as possible alternative sources of plant secondary metabolites.