The molecular circuit of steroid signalling in plants.

Steroid hormones are key regulators of growth and physiology in both plants and animals. The plant steroid hormones known as brassinosteroids (BRs) are essential for a wide range of developmental processes throughout the life cycle. In contrast with animal steroid hormones, which act mostly through nuclear receptors, BRs act through a cell-surface receptor kinase. The BR signal transduction pathway from the cell-surface receptor to nuclear gene expression has been elucidated in great molecular detail, and thus serves as a paradigm for receptor kinase signalling in plants. Furthermore, several mechanisms of signal integration have been identified that explain how BRs and other hormonal and environmental signals co-regulate specific developmental outputs in a synergistic or antagonistic manner.