Cytokinins regulate spatially specific ethylene production to control root growth in Arabidopsis.

Two principal growth regulators, cytokinins and ethylene, are known to interact in the regulation of plant growth. However, information about the underlying molecular mechanism and positional specificity of cytokinin/ethylene crosstalk in the control of root growth is scarce. We have identified the spatial specificity of cytokinin-regulated root elongation and root apical meristem (RAM) size, both of which we demonstrate to be dependent on ethylene biosynthesis.

Exploring the Binding Affinity of the ARR2 GARP DNA Binding Domain via Comparative Methods.

Plants have evolved signaling mechanisms such as the multi-step phosphorelay (MSP) to respond to different internal and external stimuli. MSP responses often result in gene transcription regulation that is modulated through transcription factors such as B-type Arabidopsis response regulator (ARR) proteins. Among these proteins, ARR2 is a key component that is expressed ubiquitously and is involved in many aspects of plant development.

New Insights into Multistep-Phosphorelay (MSP)/ Two-Component System (TCS) Regulation: Are Plants and Bacteria that Different?

The 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.

ARR22 overexpression can suppress plant Two-Component Regulatory Systems.

In plants, several developmental processes are co-coordinated by cytokinins via phosphorylation dependent processes of the Two-Component System (TCS). An outstanding challenge is to track phosphorelay flow from cytokinin perception to its molecular outputs, of which gene activation plays a major role. To address this issue, a kinetic-based reporter system was expounded to track TCS phosphorelay activity in vivo that can distinguish between basal and cytokinin dependent effects of overexpressed TCS members.

Arabidopsis response regulator 22 inhibits cytokinin-regulated gene transcription in vivo.

Cytokinin signaling in Arabidopsis is carried out by a two-component system (TCS) multi-step phosphorelay mechanism that involves three different protein families: histidine kinases (AHKs), phosphotransfer proteins (AHPs), and response regulators (ARRs) that are in turn, subdivided into A-, B- and C-type ARRs depending on their function and structure. Upon cytokinin perception, AHK proteins autophosphorylate; this phosphate is then transferred from the AHKs to the AHPs to finally reach the ARRs. When B-type ARRs are activated by phosphorylation, they function as transcription factors that regulate the expression of cytokinin-dependent genes such as the A-type ARRs, among many others.