Data from: Identification of anti-fungal bioactive terpenoids from the bioenergy crop switchgrass (Panicum virgatum)

Plant derived bioactive small molecules have attracted attention of
scientists across fundamental and applied scientific disciplines. We seek
to understand the influence of these phytochemicals on functional
phytobiomes. Increased knowledge of specialized metabolite bioactivities
could inform strategies for sustainable crop production. We hypothesized
that – consistent with accumulating evidence that switchgrass genotype
impacts microbiome assembly – differential terpenoid accumulation
contributes to switchgrass ecotype-specific microbiome composition. An
initial in vitro plate-based disc diffusion screen of 18 switchgrass root
derived fungal isolates revealed differential responses to upland- and
lowland-isolated metabolites. To identify specific fungal
growth-modulating metabolites, we tested fractions from root extracts on
three ecologically important fungal isolates – Linnemania elongata,
Trichoderma sp. and Fusarium sp. Saponins and diterpenoids were identified
as the most prominent antifungal metabolites. Finally, analysis of liquid
chromatography-purified terpenoids revealed fungal inhibition structure –
activity relationships (SAR). Saponin antifungal activity was primarily
determined by the number of sugar moieties – saponins glycosylated at a
single core position were inhibitory whereas saponins glycosylated at two
core positions were inactive. Saponin core hydroxylation and acetylation
were also associated with reduced activity. Diterpenoid activity required
the presence of an intact furan ring for strong fungal growth inhibition.