Abstract
Surveys of foliar endophytes from the Acadian forest region over the past three decades have identified numerous phylogenetically diverse fungi producing natural products toxic to forest pests and diseases. The life histories of some conifer endophytes can be restricted to plant foliage or may include saprotrophic phases on other plants tissues or even alternate hosts. Considering the potentially broad host preferences of conifer endophytes we explored fungi isolated from understory species and their metabolites as part of an ongoing investigation of fungal biodiversity from the Acadian forest. We report a hitherto unidentified Xylariomycetidae species isolated from symptomatic Labrador tea (Rhododendron groenlandicum) leaves and mountain laurel (Kalmia latifolia) collected in coastal southern New Brunswick, Canada. Morphological and phylogenetic evidence demonstrated the unknown species was a novel Synnemapestaloides (Sporocadaceae) species, described here as Syn. ericacearum. A preliminary screening assay indicated that the culture filtrate extract of the new species was potently antifungal towards the biotrophic pathogen Microbotryum violaceum, warranting an investigation of its natural products. Two natural products possessing a rare 1,3-benzodioxin-4-one scaffold, synnemadoxins A-B (1–2), and their postulated precursor, synnemadiacid A (3), were characterized as new structures and assessed for antimicrobial activity. All isolated compounds elicited in vitro inhibitory antifungal activity towards M. violaceum at 2.3 μg mL-1 and moderate antibiotic activity. Further, the characterization of synnemadoxins A-B provided a perspective on the biosynthesis of some related 1,3-benzodioxin-4-ones produced by other fungi within the Xylariales.
Highlights
Foliar endophytes of conifers in the Acadian forest of Eastern Canada have proven an exceptionally rich source of structurally diverse biologically active natural products [1,2]
Both isolates were sterile on all media tested; sporulation by one strain (DAOMC 250336) was induced when malt extract agar (MEA) blocks containing mycelia were floated in sterile water
This species is morphologically similar to Seimatosporium (Sporocadaceae), a plurivorous genus including several species described from hosts in the Ericaceae, for example Seim. arbuti, Seim. ledi, and Seim. rhododendri on Rhododendron [7,8]
Summary
Foliar endophytes of conifers in the Acadian forest of Eastern Canada have proven an exceptionally rich source of structurally diverse biologically active natural products [1,2]. Phialocephala scopiformis is a common Picea endophyte that produces its sexual reproductive structures (apothecia) on decaying Picea wood and fallen branches [3]. While considering the potentially broad host preferences of conifer endophytes, an unidentified species in Xylariomycetidae was isolated from symptomatic Rhododendron groenlandicum leaves. Morphological and phylogenetic analyses indicated this strain, as well as a conspecific strain isolated from symptomatic Kalmia latifolia leaves, represented a novel Synnemapestaloides (Sporocadaceae) species. From the culture filtrate extract of Syn. ericacearum DAOMC 250336, three new natural products, including two metabolites possessing a rare 1,3-benzodioxin-4-one scaffold, were structurally characterized and assessed for antimicrobial activity
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