Metabolomic and transcript level changes reveal the role of polyphenols and flavonols in response to Plasmodiophora brassicae infection in Brassica napus.

Secondary plant metabolites such as polyphenols and flavonols play an important role in plant defense and host–pathogen interaction. In this study, metabolomics and quantitative gene expression analysis was used to identify the polyphenols and flavonols, and the genes involved in resistance to clubroot disease in Brassica napus. For this, a set of clubroot susceptible and resistant canola lines, carrying resistance of the rutabaga cv. Polycross was inoculated with a virulent Plasmodiophora brassicae pathotype 3A to examine disease progression at 7-, 14- and 21 days after inoculation (DAI). The root samples collected at these time points were used for metabolomics and quantitative gene expression analyses. An increased concentration of several metabolites such as caffeic acid, protocatechuic aldehyde, vanillin and kaempferol, derived from phenylpropanoid and flavonoid biosynthesis pathways, were observed in roots of the resistant lines in response to P. brassicae infection implying that they might play a role in clubroot resistance. The higher expression of the genes C4H-A, C4H-B, CCR, CHI, CHS and F3H involved in the biosynthesis of these compounds substantiated the metabolomics analysis results. Conversely, significantly greater contents of ferulic acid and 3,4-hydroxybenzoic acid were found in roots of the susceptible lines indicating their possible role in disease susceptibility. Thus, the results from this study provide an insight into Brassica-P. brassicae interaction and the molecular basis of clubroot resistance. [ABSTRACT FROM AUTHOR]