Integrated Analysis of Metabolome and Transcriptome Reveals the Effect of Burdock Fructooligosaccharide on the Quality of Chinese Cabbage (Brassica rapa L. ssp. Pekinensis)

Burdock fructooligosaccharide (BFO) is fructose with a low polymerization degree, which could improve the immunity to pathogens, quality, and stress resistance of vegetables. Still, there are no studies on applying BFO in Chinese cabbage. In this study, the effects of exogenous BFO sprayed with different concentrations (0, 5, 10, 20, 30 g·L^-1) on the growth and soluble sugar content of Chinese cabbage seedlings were determined. The result showed that 10 g·L^-1 was the appropriate spraying concentration. Based on metabolome analysis, a total of 220 differentially accumulated metabolites (DAMs) were found, among which flavonoid metabolites, glucosinolate metabolites, and soluble sugar-related metabolites were the key metabolites involved in improving the quality of Chinese cabbage caused by BFO. Further combination analysis with transcriptome, trans-cinnamate 4-monooxygenase (<i>CYP73A5</i>), and chalcone synthase 1 (<i>CHS1</i>) were more closely associated with the DAMs of flavonoid biosynthesis. Sulfotransferases 18 (<i>SOT18</i>), Branched-chain amino acid amino transferases 6 (<i>BCAT6</i>), and cytochrome P450 monooxygenase (<i>CYP83A1</i>) were the key genes in glucosinolate biosynthesis. Hexokinase (<i>HxK1</i>), beta-glucosidase 8 (<i>BGL08</i>), invertase 3 (<i>INV3</i>), beta-glucosidase 3B (<i>BGL3B</i>), and sucrose phosphate synthase 1 (<i>SPS1</i>) were significantly upregulated, potentially playing crucial roles in the soluble sugar metabolism. In conclusion, these results provided an understanding of the effects of BFO on the expression of genes and the accumulation of metabolites related to quality formation in Chinese cabbage.