Phosphate give and take

A plant hormone receptor has a split personality, revealing its kinase or phosphatase side depending on whether hormone is bound, say Ari Mähönen, Ykä Helariutta (University of Helsinki, Finland), Masayuki Higuchi, Tatsuo Kakimoto (Osaka University, Japan), and colleagues.

Plant hormones known as cytokinins, which stimulate growth and cell division, are detected by three receptors with hormone-induced histidine kinase activity. The loss of cytokinin-binding ability of one of these receptor kinases, CRE1, stunts root growth. This phenotype is suppressed, the group now finds, by mutations elsewhere within CRE1. Based on this result, they hypothesized that hormone-free CRE1 inhibits its immediate downstream elements, which can be phosphorylated by multiple histidine kinases.

A logical countermeasure to a kinase is a phosphatase. Indeed, the group shows, CRE1 is a...