Digitalis purpurea P5βR2, encoding steroid 5β‐reductase, is a novel defense‐related gene involved in cardenolide biosynthesis

Abstract

• The stereospecific 5β-reduction of progesterone is a required step for cardiac glycoside biosynthesis in foxglove plants. Recently, we have isolated the gene P5βR, and here we investigate the function and regulation of P5βR2, a new progesterone 5β-reductase gene from Digitalis purpurea. • P5βR2 cDNA was isolated from a D. purpurea cDNA library and further characterized at the biochemical, structural and physiological levels. • Like P5βR, P5βR2 catalyzes the 5β-reduction of the Δ⁴ double bond of several steroids and is present in all plant organs. Under stress conditions or on treatment with chemical elicitors, P5βR expression does not vary, whereas P5βR2 is highly responsive. P5βR2 expression is regulated by ethylene and hydrogen peroxide. • The correlation between P5βR2 expression and cardenolide formation demonstrates the key role of this gene in cardenolide biosynthesis, and therefore in the chemical defense of foxglove plants.