Brassinosteroids. Plant counterparts to animal steroid hormones?

Brassinosteroids are polyhydroxylated derivatives of common plant membrane sterols such as campesterol. They occur throughout the plant kingdom and have been shown by genetic and biochemical analyses to be essential for normal plant growth and development. Numerous reviews have detailed the recent progress in our understanding of the biosynthesis, physiological responses, and molecular modes of action of brassinosteroids. It is clear that like their animal steroid counterparts, brassinosteroids have a defined receptor, can regulate the expression of specific genes, and can orchestrate complex physiological responses involved in growth. This review summarizes the current status of BR research, pointing out where appropriate the similarities and differences between the mechanism of action of brassinosteroids and the more thoroughly studied animal steroid hormones.