Biosynthetic Pathway and Bioactivity of Vanillin, a Highly Abundant Metabolite Distributed in the Root Cortex of Tea Plants (Camellia sinensis)

Volatiles are important for plant root stress resistance. The diseases in tea root are serious, causing major losses. The volatile composition in tea root and whether it can resist diseases remain unclear. In this study, the volatile composition in different tea tissues was revealed. The vanillin content was higher in the root (mainly in root cortex) than in aerial parts. The antifungal effects of vanillin on pathogenic fungi in tea root were equal to or greater than those of other metabolites. O-methyltransferase (CsOMT), a key enzyme in one of two biosynthetic pathways of vanillin, converted protocatechualdehyde to vanillin in vitro. Furthermore, its characteristics and kinetic parameters were studied. In Arabidopsis thaliana protoplasts, the transiently expressed CsOMT was localized in the cytoplasm and nucleus. These findings have clarified the formation and bioactivities of volatiles in tea roots and provided a theoretical basis for understanding how tea plants resist root diseases.