Phosphorelay signal transduction: the emerging family of plant response regulators

Homologs of bacterial two-component signal transduction elements are emergi ng as key players in eukaryotic signaling systems. The recent identificatio n of a large gene family in Arabidopsis that is similar to two-component re sponse regulators emphasizes the importance of this signaling mechanism in plants. The understanding of the function of these response regulator genes is only rudimentary but the transcriptional induction of a subset by cytok inin suggests a role for some of these regulators in the response to this i mportant plant hormone.