ASSOCIATION OF THE ARABIDOPSIS CTR1 RAF-LIKE KINASE WITH THE ETR1 ANDERS ETHYLENE RECEPTORS

In Arabidopsis thaliana, signal transduction of the hormone ethylene i nvolves at least two receptors, ETR1 and ERS, both of which are member s of the two-component histidine protein kinase family that is prevale nt in prokaryotes, The pathway also contains a negative regulator of e thylene responses, CTR1, which closely resembles members of the Raf pr otein kinase family. CTR1 is thought to act at or downstream of ETR1 a nd ERS based on double mutant analysis; however, the signaling mechani sms leading from ethylene perception to the regulation of CTR1 are unk nown. By using the yeast two-hybrid assay, we detected a specific inte raction between the CTR1 amino-terminal domain and the predicted histi dine kinase domain of ETR1 and ERS, We subsequently verified these int eractions by using an in vitro protein association assay(s), In additi on, we determined that the amino-terminal domain of CTR1 can associate with the predicted receiver domain of ETR1 in vitro. Based on deletio n analysis, the portion of CTR1 that interacts with ETR1 roughly align s with the regulatory region of Raf kinases. These physical associatio ns support the genetic evidence that CTR1 acts in the pathway of ETR1 and ERS and suggest that these interactions could be involved in the r egulation of CTR1 activity.