Abstract
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. In cytokinin signaling, while A- and B-type ARR function is well understood, it is still unclear if C-type ARRs (ARR22 and ARR24) play a role in this mechanism. Here, we describe a novel method suitable to study TCS activity natively as an in vivo system. We also show that ARR22 inhibits gene transcription of an A-type ARR upon cytokinin treatment in vivo. Consequently, we propose that ARR22, by acting as a phosphatase on specific AHPs, disrupts the TCS phosphorelay and prevents B-type ARR phosphorylation, and thus their activation as transcription factors, explaining the observed deactivation of cytokinin-responsive genes.
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Acknowledgments
Special thanks to Caterina Brancato for maintaining the cell culture and producing the protoplasts (ZMBP, Central Facilities) and Michael Fitz for technical support (ZMBP, Plant Physiology).
The authors gratefully acknowledge the financial support from the German Research Foundation (DFG) to K.H. (grant: SFB 1101, Project B05).
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Handling Editor: Burkhard Becker
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Wallmeroth, N., Anastasia, A.K., Harter, K. et al. Arabidopsis response regulator 22 inhibits cytokinin-regulated gene transcription in vivo. Protoplasma 254, 597–601 (2017). https://doi.org/10.1007/s00709-016-0944-4
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DOI: https://doi.org/10.1007/s00709-016-0944-4