Metabolomics reveals distinct methylation reaction in MeJA elicited Nigella sativa callus via UPLC–MS and chemometrics

Cell suspension cultures are now recognized as important model for studying natural products biosynthesis and functional genomics. Nevertheless, very few studies of metabolic comparisons between cell cultures (callus) and original plants have been reported, even though the biological identity of cultured cells with the normally grown plant is of great importance. In this study, an MS-based metabolomic approach was used to compare the natural products profile of intact Nigella sativa seeds versus callus . N. sativa has been used for centuries in traditional medicine for several purposes. Its phytochemical components comprise, among others, alkaloids, saponins, flavonoids and fatty acids. Ultra performance liquid chromatography coupled to ultraviolet photodiode array detection and high resolution q-TOF mass spectrometry (UPLC–PDA–MS) was utilized to analyze the secondary product metabolome of N. sativa callus, with a total of 74 metabolites including five flavonoids, 13 hydroxycinnamates, an alkaloid, saponin and 14 fatty acids. Callus maintained the capacity to produce N. sativa phenolic subclasses, with hydroxycinnamates amounting for the major secondary metabolites in callus. Alkaloids, major constituents in Nigella genus, were detected in callus though with qualitative and quantitative differences from seed tissue. Methyl jasmonate (MeJA) elicitation effect was assessed on callus with the aim of increasing secondary metabolites production. Metabolite profiles were subjected to principal component analysis and orthogonal projection to latent structures-discriminant analysis to evaluate MeJA effect. Results revealed that MeJA led to O-methylation reaction induction yielding O-feruloylquinic acid from O-caffeoylquinic acid, in addition to a methylated disaccharide. The work extends our knowledge regarding hydroxycinnamates biosynthesis, regulation and on metabolic engineering future efforts to increase its production as potential phytoalexin in N. sativa