IN THIS ISSUE Brassinosteroid Perception and Signaling: Heterodimerization and Phosphorylation of Receptor-Like Kinases BRI1 and BAK1

Brassinosteroids (BRs) are plant growth hormones that are structurally similar to insect and animal steroids. Since the discovery of BRs in Brassica napus pollen, more than 40 BR-like compounds have been identified in numerous plant species (Altmann, 1999). BRs show a strong growth-promoting effect when applied to plants in nanomolar concentrations because of positive effects on both cell division and cell elongation. BR mutants typically show dwarfism, dark green coloration, reduced fertility, delayed senescence, and altered defense responses, suggesting roles in diverse developmental processes (Clouse and Sasse, 1998).