Abstract
Fragrant agarwood, arguably the costliest wood in the world, is formed by plant-fungal interactions in Aquilaria spp. However, very little is known about this fragrant outcome of interaction. Therefore, mimicking the ancient traditions of agarwood production in Assam (Northeast India), a chemometric assessment of the agarwood-fungus interaction was made by chemical profiling (GC-MS) coupled with statistical analysis (principal component, correlation network analysis) across three platforms, viz. callus, juvenile plants and resinous wood-chips with an associated Fusarium. In the study of callus-fungus interaction, increased accumulation of key aroma compounds such as pentatriacontane {fold change (log2FC) = 3.47)}, 17-pentatriacontene (log2FC = 2.95), tetradecane, 2-methyl- (log2FC = 1.10) over callus and activation of pathways related to defense and secondary metabolism indicated links to aroma production. Study on fungal interactions in juvenile plants and resinous wood-chips indicated formation of terpenoid precursors (e.g. farnesol, geranylgeraniol acetate) and agarwood sesquiterpenes (e.g. agarospirol, γ-eudesmol). Correlation network analysis revealed the possible regulation of sesquiterpene biosynthesis involving squalene. Also a direct role of fungus in aroma (e.g. dodecane, 4-methyl-, tetracosane) was highlighted. Appearance of fragrant molecules unknown to agarwood during interaction featured as a new possibility for future research.
Highlights
Plant based fragrances are the major constituents of commercial aroma and personal-care industry
It is believed that A. malaccensis plants only above the age of 10–15 years are suitable for resin formation, a recent report of artificial induction of agarwood in juvenile (4 year old) plants by fungal infection has opened new possibilities in agarwood production[9]
Using potato dextrose agar (PDA) as culture media, a total of 33 fungal associates were isolated from resinous tissue of agarwood (Supplementary Table ST-1)
Summary
Plant based fragrances are the major constituents of commercial aroma and personal-care industry. The growing consumer preference for natural ingredients has led to renewed interest in biogenic fragrances In this context, fragrant volatiles formed as a result of plant-microbial interactions is a potential option for the future. Biotechnological interventions including fermentation and microbial production of fragrant compounds are already being actively explored in the flavor and fragrance industry[1,2,3]. There are instances of plant-microbial associations in nature that result in formation of fragrant compounds, as in case of vetiver[4] and agarwood. Two previous studies conducted on these aspects included transcriptomics and metabolomics analyses of healthy and resinous agarwood[21,22] These studies did not focus on the plant-fungal interaction. This, apart from enhancing the basic understanding of agarwood formation can potentially broaden the base of agarwood aromatics for the future
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