Progestogens and androgens influence root morphology of angiosperms in a brassinosteroid-independent way - C21- and C19-steroids a novel class of phytohormones?

Progestogens and androgens are steroids that have been found in a broad range of plants, but little is known about their physiological function. Within this study we sowed seeds of angiosperms on progestogen- and androgen-containing medium and analyzed the morphological effects. Moreover, we analyzed the effects of progesterone and testosterone on brassinosteroid profiles and gene expression of A. thaliana. Additionally, we analyzed the effects of progesterone and testosterone on A. thaliana plants that overexpress the steroid 5α-reductase DET2. We found that progestogens and androgens have strong negative effects on root length particularly in Brassicaceae species. Moreover, these steroids led to uncoordinated cell growth and enhanced lateral root formation. We could not detect an influence on brassinosteroid profiles and gene expression of brassinosteroid-regulated genes. The overexpression of DET2 led to enhanced root growth, but the effects of progesterone and testosterone were not reduced. We conclude that progestogens and androgens act in a brassinosteroid-independent way. We see this as a hint that progestogens and androgens might be a novel class of steroidal phytohormones in plants. 7 days old A. thaliana plants were transferred to PNM medium. After 2 days of adaption to the new medium, plants were treated with 10 µM PO (dissolved in 0.12% DMSO) or 10 µM TO, while 0.12% DMSO was used as a mock treatment. Leaves were harvested after 1 h and immediately frozen in liquid nitrogen. Comparative gene expression profiling analysis using data obtained from RNA-seq of A. thaliana leaves under different conditions.