Metabolomic changes of Brassica rapa under biotic stress

Abstract

It has been shown by this thesis that plant metabolomics is a promising tool for studying the interaction between B. rapa and pathogenic fungi. It gives a picture of the plant metabolites during the interaction. Brassica rapa has many defense related compounds such as glucosinolates, IAA, phenylpropanoids and flavonoids and even some primary metabolites including amino and organic acids which might play role in resistance against pathogens. These metabolic pathways undergo rerouting during the infection and the required precursors for the defense compounds might be formed. The rerouting of fluxes at the level of chorismate seems to play a role in resistance of B. rapa to pathogenic fungi. Resistance involves a very high level of complexity. Understanding resistance thus requires studies of different combinations of cultivars and microorganisms. By taking a systems biology approach and measuring on the level of transcriptome, proteome and metabolome and analyzing the large data sets from interactions of different cultivars with different fungi in combination with data on susceptibility by means of multivariate analysis might give a better insight in the defense response of the plant. As we used different cultivars in our study, the fungal infection and also treatment with signal molecules induced secondary metabolites that branch from the chorismate pathway including phenylpropanoids, flavonoids, IAA and indole glucosinolates. Even with using different cultivars from B. rapa, all cultivars showed enhanced accumulation of secondary metabolites derived from the chorismate pathway. Phenylpropanoids, benzoyl glucosinolates, flavonoids and indole glucosinolates should be the target compounds for genetic engineering research. By using genetic engineering techniques, one can breed new cultivars that are characterized by higher levels of these secondary metabolites.