| Type: | Family | Name: | Response regulator, plant B-type |
| Description: | Members of this group are plant response regulators of the B type. B-type plant response regulators most closely resemble the classical microbial response regulators.Classical two-component signal transduction systems--consisting of a histidine protein kinase (HK) to sense signal input and a response regulator (RR) to mediate output--are widespread in prokaryotes. Their counterparts are also found in eukaryotes, indicating that they represent an ancient and evolutionarily conserved signalling mechanism. In plants, two-component systems are involved in phytohormone, stress, and light signalling [, ]. Plant response regulators (called ARRs in Arabidopsis thaliana(Mouse-ear cress)) fall into three distinct families based on domain architecture: A-type RRs are stand-alone receiver domains and, therefore, belong to (a large family of signal transduction receiver (phosphoacceptor) proteins, CheY-like), subfamily ; B-type RRs contain an N-terminal receiver domain fused to a Myb-like DNA-binding domain and a variable C-terminal domain; pseudo-response regulators () contain an atypical receiver domain.The classical microbial RRs consist of an N-terminal CheY-like receiver (phosphoacceptor) domain and a C-terminal output (usually DNA-binding) domain. In a typical microbial signal transduction system, in response to an environmental stimulus, a phosphoryl group is transferred from the His residue of sensor histidine kinase to an Asp residue in the CheY-like receiver domain of the cognate response regulator [, , ]. Phosphorylation of the receiver domain induces conformational changes that activate an associated output domain, which in turn triggers the response. Phosphorylation-induced conformational changes in response regulator molecules have been demonstrated in direct structural studies []. For more information on the receiver domain, please see and related groups.The output domain of B-type plant RRs is a central Myb-like DNA-binding domain (with the B, or GARP, motif) [, , ] which is not found in two-component prokaryotic systems. This domain is believed to be responsible for the promoter-binding and transcription factor activity of the B-type plant RRs [, ]. The B motif contains a helix-turn-helix structure and a potential nuclear localization signal, and is considered to be a multifunctional domain responsible for both nuclear localization and DNA binding [].A variable C-terminal domain may also play a role as part of the output module and provides the basis for defining several small subgroups. The functions of these unique C-terminal domains and biological significance of the subgroups are unclear. | Short Name: | Response_reg_B-typ_pln |
