Abstract
The Arabidopsis multistep-phosphorelay (MSP) is a signaling mechanism based on a phosphorelay that involves three different types of proteins: Histidine kinases, phosphotransfer proteins, and response regulators. Its bacterial equivalent, the two-component system (TCS), is the most predominant device for signal transduction in prokaryotes. The TCS has been extensively studied and is thus generally well-understood. In contrast, the MSP in plants was first described in 1993. Although great advances have been made, MSP is far from being completely comprehended. Focusing on the model organism Arabidopsis thaliana, this review summarized recent studies that have revealed many similarities with bacterial TCSs regarding how TCS/MSP signaling is regulated by protein phosphorylation and dephosphorylation, protein degradation, and dimerization. Thus, comparison with better-understood bacterial systems might be relevant for an improved study of the Arabidopsis MSP.
Highlights
The Arabidopsis multistep-phosphorelay (MSP) is a signaling mechanism based on a phosphorelay that involves three different types of proteins: Histidine kinases, phosphotransfer proteins, and response regulators
These proteins belong to two subfamilies, naming the two-component system (TCS): The histidine kinases (HK) that auto-phosphorylates a conserved histidine (His; H) residue upon signal perception, and the response regulators (RR) that are activated by accepting the phosphate on a conserved aspartate (Asp; D) residue from the HK [1,2]
The number and character of the proteins involved in a phosphorelay can strongly vary—especially in the bacterial TCS, entailing several HK, His-containing phosphotransfer protein (HPt), or RRs [8]—the nature of the phosphorelay remains constant and phosphates are transferred from His-to-Asp residues at all times [2,7] (Figure 1)
Summary
The Arabidopsis multistep-phosphorelay (MSP) is a signaling mechanism based on a phosphorelay that involves three different types of proteins: Histidine kinases, phosphotransfer proteins, and response regulators. Using the model plant Arabidopsis, I focused on three different mechanisms that both bacteria and plants use to finetune TCS/MSP signaling: RR’s protein degradation, protein dephosphorylation, and protein dimerization. Plant systems provide examples where RRs proteolysis results in a mechanism to control MSP signaling.
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