Expression Analysis of Gene Encoding 1-Deoxy-d-Xylulose 5-Phosphate Reductoisomerase (DXR) and Cardenolide and Digitoxin Production in Digitalis purpurea L. Using Polyamines and Methyl Jasmonate as Elicitors

Digitoxin is a glycoside isolated from leaves of various species of Digitalis genus that are commonly called foxgloves. Digitoxin is used for chronic cardiac insufficiency, tachyarrhythmia form of atrial fibrillation, paroxysmal ciliary arrhythmia, and paroxysmal supraventricular tachycardia. 1-Deoxy-d-Xylulose 5-phosphate Reductoisomerase (DXR) is an important rate-limiting enzyme in 2-C-Methyl-d-Erythritol 4-Phosphate (MEP) pathway, and expression level of DXR plays a critical role in control of plant isoprenoid biosynthesis pathway. The effects of different elicitors including putrescine, spermine, and spermidine at concentrations of 50 and 100 mg L-1 and also Methyl Jasmonate (MJ) at 50, 100, and 200 μM concentrations were explored on transcript levels of DXR gene in cell suspension culture of foxglove (Digitalis purpurea). DXR transcription levels were assessed by the semi-quantitative RT-PCR. Results showed that elicitors had significant effects on the expression level of DXR and contents of cardenolide and digitoxin. The highest digitoxin (61.3 μg g-1 DW) and cardenolide (1.48% mg-1 DW) content was observed in 100 mg L-1 spermidine treatment. In all treatments, the expression of DXR gene was increased compared with the control sample. The highest transcription levels of DXR gene was observed in 50 μM MJ and 100 mg L-1 putrescine elicitors, which was nine folds higher than the control condition, and the lowest levels were observed for putrescine treatments at concentrations of 50 and 100 mg L-1, respectively.