Fungal infection-induced metabolites in Brassica rapa

The metabolic interactions between three cultivars of Brassica rapa and three pathogenic fungi such as Leptosphaeria maculans, Aspergillus niger, and Fusarium oxysporum were investigated using 1H nuclear magnetic resonance spectroscopy. Firstly, in order to reveal latent information on common metabolites induced by these fungi, partial least square-discriminant analysis (PLS-DA) was applied to the 1H NMR spectra of fungi-infected and control plants of the three cultivars. It showed the presence of metabolites in infected B. rapa leaves such as phenylpropanoids, flavonoids and glucosinolates which were highly associated with the fungal infection. Subsequently, the difference between the metabolic responses to each type of fungal infection was evaluated. F. oxysporum infected plants were found to accumulate more phenylpropanoids (sinapoyl-, feruloyl- and 5-hydroxyferuloyl malate), flavonoids (kaempferol and quercetin) and fumaric acid than the infection of other two fungal species. In addition to the variation depending on fungal species, the cultivars of host plant largely affect the metabolic alteration. Nuclear magnetic resonance (NMR)-based metabolomics employed in this study reveals that fungal infection alters a manifold of secondary metabolites, though specific patterns were observed for each fungus and each cultivar.