Iridoid profiles and expression patterns of iridoid-related biosynthetic genes in three Nepeta nuda L. accessions

Abstract

Nepeta nuda L. (family Lamiaceae) is a widespread species characterized by the prevalence of bioactive specialized metabolites from the groups of iridoids and phenolic. Analyzed plants were grown in vitro and in greenhouse from seeds collected from eastern Serbia (“Debeli Lug”), obtained from other research groups (“Rhodopes”, Bulgaria), or commercially purchased (“Jellito”, Germany). The chemical composition of N. nuda leaves was analyzed using the UHPLC/DAD/(±)HESI±МS2 method, targeted towards dominant iridoid compounds. Both in vitro and greenhouse grown plants are rich in iridoid glycoside 1,5,9-epideoxyloganic acid (1,5,9– eDLA), and among analysed accessons N. nuda “Debeli Lug” was pointed out as the most productive one. When it comes to iridoid aglycones, it is noticeable that N. nuda “Jelitto” biosynthetizes cis, trans- isomer of nepetalactone (NL) while N. nuda “Rhodopes” and N. nuda “Debeli Lug” possess cis,cis-NL. Relative expression of early biosynthetic genes- EBGs (NnGPPS, NnGES, NnG80, Nn8HGO), in plants grown in vitro, is much higher in N. nuda “Debeli Lug“ accession, compared to N. nuda “Rhodopes” and N.nuda “Jellito”. In greenhouse grown plants, there is no particular regularity when it comes to the expression of EBGs in three N. nuda accessions. NEPS enzymes seem to be one of the key factors determining the metabolic flux and productivity of N. nuda. While plants grown in vitro and in greenhouse both express NnNEPS2, only plants grown in vitro express NnNEPS1.2. It is also noticeable that N. nuda “Debeli Lug“ accession displays the highest NnNEPS2 expression, and the lowest NnNEPS1.2 expression.