Metabolomics approach in identifying biomarkers from pathogenic Ganoderma boninense involved in early interactions with oil palm host

This study attempts to identify key biomarkers that may be involved in the early interactions of oil palm and Ganoderma boninense. To achieve this, the oil palm extract medium (OPEM) was adopted as a model to simulate oil palm-Ganoderma interactions in planta with biomarkers identified using the LC-MS-based metabolomics approach. The metabolic profiles of ethyl acetate crude extracts of OPEM and G. boninense-inoculated OPEM (OPEM + Gb, incubated for 1, 3, 7, 14, 21 and 28 days) were compared using liquid chromatography quadrupole/time-of-flight-mass spectrometry (LC-Q/TOF-MS) coupled with multivariate data analysis using the platform MetaboAnalyst. Results revealed that the OPEM constituents such as kakuol, kanokoside A, abruquinone B and robinetin 3-rutinoside are naturally occurring plant metabolites and may be involved in defense mechanisms against G. boninense. By contrast, aspulvinone H and methylisocitric acid were produced by G. boninense and may be precursors for the synthesis of other compounds that contribute to successful disease infection. Additionally, the metabolomics analyses further ranked 15 important secondary metabolites according to their variable importance in projection (VIP) scores. These compounds comprise one ketone, two fatty acids, two flavonoids and, one isomer and nine unknowns that are suggestive of early plant-pathogen interactions. These 15 compounds were further analysed using a heatmap revealing decreased concentrations of plant-derived metabolites kakuol, kanokoside A and 5,7,4ʹ-trihydroxy-3,6,8,3ʹ,5ʹ-pentamethoxyflavone and increased concentrations of plant-derived fatty acids 9-hydroxy-hexadecan-1,16-dioic acid and 11-hydroperoxy-12,13-epoxy-9-octadecenoic acid in the presence of G. boninense. Changes in the concentrations of these compounds suggest the presence of G. boninense, thereby indicating early infections in the oil palm. These biomarkers may be further developed as a rapid and non-invasive diagnostic for early detection of Ganoderma infection in oil palm.