Expression of cardenolide-biosynthetic genes under stress conditions

Cardenolides, like many other small plant natural products, may play a role in plant defense by acting as deterrents to herbivores (Berglund & Ohlsson, 1992). As for humans cardenolides have a long tradition in the therapy of cardiac insufficiency (Mutschler, 2008). New therapeutic roles for cardenolides in various diseases are discussed. Among them, the susceptibility of cancer cells to cardenolides in tumor therapy is of special interest (Newman et al., 2008). Cardenolides are still isolated from plants since their structural complexity impede their chemical synthesis. Their biosynthesis is affected by phytohormones, abiotic and biotic stress (Pérez-Bermúdez et al., 2009). Improving cardenolide production requires a detailed knowledge of their biosynthesis. To understand the regulation of genes encoding enzymes involved in cardenolide biosynthesis their differential expression under stress conditions was investigated in two different plant species, namely Digitalis lanata and Erysimum crepidifolium. Over decades cardenolide biosynthesis was mainly investigated in Digitalis. Therefore, we started our investigations with D. lanata shoot cultures. Stress was induced by permanent darkness and addition of bioactive enones. The expression of several genes was monitored, namely progesterone 5β-reductases 1 and 2 (P5βR,P5βR2), 3β-hydroxysteroiddehydrogenase 1 (3βHSD1) and actin (as a control). All genes showed a constant expression except for P5βR2, which was subject to fluctuations and inducable by bioactive enones. Because of its close relationship to Arabidopsis thaliana, Erysimum crepidifolium was established as a new model plant to study cardenolide biosynthesis (Munkert et al., 2011). E. crepidifolium shoot cultures were established and cardenolide formation as well as differential gene expression after stress induction of the genes mentioned above were also investigated in the new system.