RESPONSE REGULATORS IMPLICATED IN HIS-TO-ASP PHOSPHOTRANSFER SIGNALING IN ARABIDOPSIS

The His to Asp phosphotransfer signal transduction mechanism involves three common signaling domains: the transmitter (or His-kinase), the r eceiver, and the histidine-containing phototransfer (HPt) domain, Typi cally, a sensor kinase has a His-kinase domain and a response regulato r has a receiver domain containing a phosphoaccepting aspartate, where as a histidine-containing phototransfer domain serves as a mediator of the histidine-to-aspartate phosphotransfer. This signal transduction mechanism was thought to be restricted to prokaryotes. However, many e xamples have been discovered in diverse eukaryotic species including h igher plants, In Arabidopsis, three sensor kinases have been character ized, namely, ETR1, ERS, and CKI1, which were suggested to be involved in ethylene-and cytokinin-dependent signal transduction pathways, res pectively. To date, no response regulator has been discovered in highe r plants, We identify five distinct Arabidopsis response regulator gen es, each encoding a protein containing a receiver-like domain, In vivo and in vitro evidence that ARRs can function as phosphoaccepting resp onse regulators was obtained by employing the Escherichia coil His-Asp phosphotransfer signaling system.