The response regulator 2 mediates ethylene signalling and hormone signal integration

Hormones are important regulators of plant growth and development. In Arabidopsis, perception of the phytohor-mones 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 signal-ling component functioning downstream of ETR1 in ethy-lene 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 mediat-ing ethylene responses. Additional investigations indicate that an ETR1-initiated phosphorelay regulates the tran-scription 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-compo-nent network that interferes with a multitude of different signalling pathways and thereby contributes to the highly integrated signal processing machinery in higher plants