The response regulator 2 mediates ethylene signalling and hormone signal integration in Arabidopsis

Hormones are important regulators of plant growth and development. In Arabidopsis , perception of the phytohormones ethylene and cytokinin is accomplished by a family of sensor histidine kinases including ethylene‐resistant (ETR) 1 and cytokinin‐response (CRE) 1. We identified the Arabidopsis response regulator 2 (ARR2) as a signalling component functioning downstream of ETR1 in ethylene signal transduction. Analyses of loss‐of‐function and ARR2‐overexpressing lines as well as functional assays in protoplasts indicate an important role of ARR2 in mediating ethylene responses. Additional investigations indicate that an ETR1‐initiated phosphorelay regulates the transcription factor activity of ARR2. This mechanism may create a novel signal transfer from endoplasmic reticulum‐associated ETR1 to the nucleus for the regulation of ethylene‐response genes. Furthermore, global expression profiling revealed a complex ARR2‐involving two‐component network that interferes with a multitude of different signalling pathways and thereby contributes to the highly integrated signal processing machinery in higher plants.