Expression analysis of key enzymes involved in the accumulation of iridoid in Rehmannia glutinosa

As the traditional Chinese herb, Rehmannia glutinosa (R. glutinosa) has significant effects on health. The main active ingredient of R. glutinosa is iridoid. In this study, root, stem and leaf of R. glutinosa at five different growth stages were collected, the content of iridoid in R. glutinosa was determinated, and the expression of key enzymes in R. glutinosa was analyzed by quantitative real-time PCR (q-PCR). We found that the content of iridoid was increased continuously during the first three growth stages (I-III) of R. glutinosa. It reached the maximum value in root and leaf at growth stage III of R. glutinosa. However, the content of iridoid was not lower in leaf, compared with root. 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), Geranyl pyrophosphate synthase (GPPS), Geraniol 10-hydroxylase (G10H) and 10-hydroxygeraniol oxidoreductase (10HGO) were the key enzymes involved in the synthesis of iridoid in plant, but their expression pattern or level was different in various tissues and stages of R. glutinosa. All appeared tissue specificity and their expression was related to the accumulation of iridoid in R. glutinosa. Thus, DXR, GPPS, G10H and 10HGO might take part in the synthesis of iridoid in R. glutinosa and could be differently regulated during the growth and development of R. glutinosa, which would provide theoretical basis for the research on secondary metabolism of iridoid in R. glutinosa.