Figure 9.

Pathways flagged from metabolomics analysis using MetaboAnalyst software. Signatory metabolites involved in each pathway are illustrated in the form of pie charts according to their relative intensities and presence across the different cultivars and treated groups. (A) The phenylpropanoid pathway, (B) the flavonoid pathway overlapping with the phenylpropanoid pathway (*), and (C) the linoleic acid pathway that showed the highest impact after pathway enrichment analysis, along with (D), the general secondary metabolite biosynthesis pathway. Some limitations in MetaboAnalyst prevented the mapping of all annotated metabolites (Table 1). The different colours indicate “Dunnart” infected (pink), “Dunnart control” (dark green), “SWK001” infected (red) and “SWK001” control (light green). The metabolites synthesised via the phenylpropanoid-and flavonoid pathways are some of the most widely occurring secondary metabolites that are involved in plant development and defence against abiotic and biotic stresses, such as phenolics, flavonoids, coumarins and lignin [45,46]. Both pathways are initiated with the conversion of phenylalanine to p-coumaroyl-CoA and have some overlap, as shown (*) in Figure 9B. The presence and distribution of the phenolic compounds, from both the phenylpropanoid and flavonoid pathways, across the plant kingdom at a cellular, tissue and organ level emphasises the vast biological and biochemical functions important to the survival of plants [47,48]. Phenolics have been known to play important roles in plant-pathogen interactions as either pre-formed (phytoanticipins) or induced anti-pathogenic molecules (phytoalexins) [49]. Linoleic acids (C18:2) are unsaturated fatty acids that are prevalent in plant membranes, hence making them important for plant structure and maintaining water permeability and, additionally, are involved in the formation of jasmonate, which act as signalling molecules in response to tissue damage caused by insects, pathogens, herbivores or mechanical stress [50].