Identification and analysis of phenylpropanoid biosynthetic genes and phenylpropanoid accumulation in watercress (Nasturtium officinale R. Br.)

Abstract

Watercress (Nasturtium officinale R. Br.) is a cruciferous plant consumed by people worldwide. This vegetable contains numerous health-benefiting compounds; however, gene information and metabolomic profiling of individual parts for this plant species are scarce. In this study, we investigated the expression patterns of phenylpropanoid biosynthetic genes and the content of phenylpropanoids in different parts of watercress. We identified 11 genes encoding enzymes related to the phenylpropanoid biosynthetic pathway and analyzed the expression patterns of these genes in the leaves, stems, roots, flowers, and seeds of watercress. The result showed that most of the genes were expressed at the highest levels in the flowers. HPLC analysis performed in samples from these same parts revealed the presence of seven phenylpropanoid-derived compounds. The content of total phenylpropanoids was the highest in flowers, followed by that in the leaves, whereas the lowest level was generally detected in the stems. Rutin was the most abundant phenylpropanoid in all plant segments, while quercetin was detected only in the flowers and roots. This study provides useful information for further molecular and functional research involving N. officinale and closely related species.

Keywords: HPLC metabolite analysis; Nasturtium officinale; Phenylpropanoid; Phenylpropanoid biosynthetic genes; Watercress.

Fig. 1

The phenylpropanoid biosynthetic pathway in plants. PAL phenylalanine ammonia-lyase; C4H cinnamate 4-hydroxylase; 4CL 4-coumaryl-CoA ligase; CHS, chalcone synthase; CHI chalcone isomerase; F3H, flavanone-3-hydroxylase; F3′H flavonoid-3′-hydroxylase; FLS flavonol synthase; GT glucosyltransferase; RT 3-O-rhamnosyltransferase; COMT caffeic O-methyltransferase; HQT hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase; C3H 4-coumarate 3-hyroxylase

Fig. 2

Expression of phenylpropanoid biosynthetic genes in different parts of N. officinale. Gene expression was measured in 2-month-old plants. Ubiquitin-conjugating enzyme 9 gene (UBC9) was used as a reference gene. Each value is the mean of three replicates, and error bars indicate standard deviation (SD). Letters a-e denote significant differences (p < 0.05)