title: UV-B modulates the interplay between terpenoids and flavonoids in peppermint (Mentha x piperita L.).
abstract: Modulation of secondary metabolites by UV-B involves changes in gene expression, enzyme activity and accumulation of defence metabolites. After exposing peppermint (Mentha x piperita L.) plants grown in field (FP) and in a growth chamber (GCP) to UV-B irradiation, we analysed by qRT-PCR the expression of genes involved in terpenoid biosynthesis and encoding: 1-deoxy-D-xylulose-5-phosphate synthase (Dxs), 2-C-methyl-D-erythritol-2,4-cyclodiphosphate synthase (Mds), isopentenyl diphosphate isomerase (Ippi), geranyl diphosphate synthase (Gpps), (-)-limonene synthase (Ls), (-)-limonene-3-hydroxylase (L3oh), (+)-pulegone reductase (Pr), (-)-menthone reductase (Mr), (+)-menthofuran synthase (Mfs), farnesyl diphosphate synthase (Fpps) and a putative sesquiterpene synthase (S-TPS). GCP always showed a higher terpenoid content with respect to FP. We found that in both FP and GCP, most of these genes were regulated by the UV-B treatment. The amount of most of the essential oil components, which were analysed by gas chromatography-mass spectrometry (GC-MS), was not correlated to gene expression. The total phenol composition was found to be always increased after UV-B irradiation; however, FP always showed a higher phenol content with respect to GCP. Liquid chromatography-mass spectrometry (LC-ESI-MS/MS) analyses revealed the presence of UV-B absorbing flavonoids such as eriocitrin, hesperidin, and kaempferol 7-O-rutinoside whose content significantly increased in UV-B irradiated FP, when compared to GCP. The results of this work show that UV-B irradiation differentially modulates the expression of genes involved in peppermint essential oil biogenesis and the content of UV-B absorbing flavonoids. Plants grown in field were better adapted to increasing UV-B irradiation than plants cultivated in growth chambers. The interplay between terpenoid and phenylpropanoid metabolism is also discussed.
authors.affiliation: Department of Plant Biology, University of Turin, Innovation Centre, Turin, Italy.
authors.forename: Yuliya
authors.initials: Y
authors.lastname: Dolzhenko
authors.forename: Cinzia M
authors.initials: CM
authors.lastname: Bertea
authors.forename: Andrea
authors.initials: A
authors.lastname: Occhipinti
authors.forename: Simone
authors.initials: S
authors.lastname: Bossi
authors.forename: Massimo E
authors.initials: ME
authors.lastname: Maffei
mesh_terms: D002851:Chromatography, High Pressure Liquid; D044950:Flavanones / Q000032:analysis; D005419:Flavonoids / Q000032:analysis* / Q000096:biosynthesis; D018506:Gene Expression Regulation, Plant; D006569:Hesperidin / Q000032:analysis; D036142:Mentha piperita / Q000378:metabolism / Q000528:radiation effects*; D009822:Oils, Volatile / Q000378:metabolism; D010636:Phenols / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013729:Terpenes / Q000032:analysis* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D044950:Flavanones; D005419:Flavonoids; D009822:Oils, Volatile; D010636:Phenols; D010940:Plant Proteins; D013729:Terpenes; C114706:eriocitrin; D006569:Hesperidin