Age-related variation of polyphenol content and expression of phenylpropanoid biosynthetic genes in Agastache rugosa

Agastache rugosa (Fisch. & C.A.Mey.) Kuntze is an East Asian medicinal and aromatic crop rich in bioactive polyphenols, but their content is highly variable. To get insight into mechanisms regulating the biosynthesis of phenolics, leaves of one-, two- and three-year-old A. rugosa and their mother plants, were analyzed for phytochemical profile and key biosynthetic genes expression. Using UHPLC-QTOF-MS thirty-six polyphenolic compounds were found, out of which twelve were quantified. The major compounds (rosmarinic acid, apigenin glucoside, chlorogenic acid) content differed significantly between plants of different age and different age of their mother plant as confirmed by multivariate statistics. There was also a close relationship between one-year old plant groups and their respective plant progenitors which suggests an existence of a transgenerational phenomenon. Quantitative real-time PCR showed that transcript levels of: phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate: CoA ligase (4CL), tyrosine aminotransferase (TAT), hydroxyphenylpyruvate reductase (HPPR), chalcone synthase (CHS) and chalcone isomerase (CHI) did not reflect end-product concentrations. Only expression of rosmarinic acid synthase (ArEAS) correlated with its end-product accumulation. We propose that ArRAS is the rate-limiting step for RA biosynthesis in A. rugosa.