Age-related variation in polyphenol content and expression of phenylpropanoid biosynthetic genes in a medicinal and aromatic perennial Agastache rugosa

Agastache rugosa (Fisch. & C.A.Mey.) Kuntze is an East Asian medicinal and aromatic herb rich in bioactive polyphenols, but its phytochemical composition is highly variable.

To elucidate potential factors which may cause the variability of the profile of pharmacologically useful phenylpropanoids, we studied the phytochemical profile and gene expression in leaves of one-, two- and three-year-old field grown A. rugosa and their mother plants. Using UHPLC−qTOF-MS thirty six different polyphenolic compounds were detected in A. rugosa leaves, out of which twelve were quantified. The quantities of the three major compounds (rosmarinic acid - RA, apigenin glucoside, chlorogenic acid) differed significantly between plant groups of different age and different age of a mother plant as confirmed by the PCA and PLS analyses. There was also a close relationship between one-year old plant groups and their respective progenitors which suggests an existence of a transgenerational phenomenon.

Quantitative real-time PCR analysis showed that 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) transcript levels do not reflect end-product concentrations. Among the analyzed phenylpropanoid biosynthetic genes ArRAS (encoding rosmarinic acid synthase) was identified to be the rate-limiting step for RA biosynthesis in field grown A. rugosa. Thus, we identified ArRAS as a putative functional candidate for further characterisation via i.e. reverse genetic approaches to practically control rosmarinic acid production.