Plant hormone receptors: perception is everything.

Despite the bewildering ability of higher plants to change their development with respect to the environment, there appear to be only a few hormones that function to organize growth and development. With the recent identification of three plant hormone receptors, the molecular identities of all the major plant receptors are now known. Some plant hormones such as cytokinins, ethylene, and brassinosteroids (BR) use well-characterized signaling modules such as those involving receptor kinases, but in the case of the ethylene and BR receptors, there appear to be additional functions aside from the hormone they perceive. Auxin and gibberellin perception require unique mechanisms where the receptors are components involved in ubiquitination-dependent proteolysis. With plant hormone receptors in hand, comparisons can now be made between plants and other kingdoms as to how hormones control growth and development.