Progestogens and androgens influence root morphology of angiosperms in a brassinosteroid-independent manner

Progestogens and androgens are steroids found in a wide range of plants, but little is known about their physiological functions. In this study, we sowed seeds of angiosperms on progestogen- and androgen-containing medium and analysed their morphological effects. We further investigated the effects of progesterone and testosterone on brassinosteroid profiles and gene expression in A. thaliana. Additionally, we examined the effects of progesterone and testosterone on A. thaliana plants overexpressing the steroid 5α-reductase DET2. We found that progestogens and androgens have strong negative effects on root length, especially in Brassicaceae species. In addition, these steroids led to uncoordinated cell growth and increased lateral root formation. We failed to detect an effect on endogenous brassinosteroid levels and gene expression of brassinosteroid-regulated genes. The overexpression of DET2 led to increased root growth, but the effects of progesterone and testosterone were not reduced. We conclude that progestogens and androgens act in a brassinosteroid-independent manner. This suggests that progestogens and androgens could represent a potential new class of plant steroid signalling molecules.