Arabidopsis Response Regulator1 and Arabidopsis Histidine Phosphotransfer Protein2 (AHP2), AHP3, and AHP5 Function in Cold Signaling

Jin Jeon,Jungmook Kim

doi:10.1104/pp.112.207621

Abstract

The Arabidopsis (Arabidopsis thaliana) two-component signaling system, which is composed of sensor histidine kinases, histidine phosphotransfer proteins, and response regulators, mediates the cytokinin response and various other plant responses. We have previously shown that ARABIDOPSIS HISTIDINE KINASE2 (AHK2), AHK3, and cold-inducible type A ARABIDOPSIS RESPONSE REGULATORS (ARRs) play roles in cold signaling. However, the roles of type B ARRs and ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEINS (AHPs) have not been investigated in cold signaling. Here, we show that ARR1 and AHP2, AHP3, and AHP5 play positive roles in the cold-inducible expression of type A ARRs. arr1 mutants showed greatly reduced cold-responsive expression of type A ARRs compared with the wild type, whereas ARR1-overexpressing Arabidopsis exhibited the hypersensitive cold response of type A ARRs as well as enhanced freezing tolerance with cytokinin, suggesting that ARR1 functions as a positive factor of cold signaling. Transgenic Arabidopsis expressing ARR1ΔDDK:GR lacking the amino-terminal receiver domain showed wild-type expression levels of type A ARRs in response to cold, indicating that the signal receiver domain of ARR1 might be important for cold-responsive expression of type A ARRs. ahp2 ahp3 ahp5 triple mutations greatly reduced type A ARR expression in response to cold, whereas the single or double ahp mutants displayed wild-type levels of ARR expression, suggesting that AHP2, AHP3, and AHP5 are redundantly involved in cold signaling. Taken together, these results suggest that ARR1 mediates cold signal via AHP2, AHP3, or AHP5 from AHK2 and AHK3 to express type A ARRs. We further identified a cold transcriptome affected by ahk2 ahk3 mutations by microarray analysis, revealing a new cold-responsive gene network regulated downstream of AHK2 and AHK3.

Highlights

The Arabidopsis (Arabidopsis thaliana) two-component signaling system, which is composed of sensor histidine kinases, histidine phosphotransfer proteins, and response regulators, mediates the cytokinin response and various other plant responses
To determine whether type B ARABIDOPSIS RESPONSE REGULATORS (ARRs) are involved in cold-inducible expression of type A ARRs, we analyzed the expression of ARR5, ARR6, ARR7, and ARR15 in type B arr1, arr10, or arr12 single T-DNA insertional mutants as well as in multiple mutants in response to cold by using the quantitative reverse transcription (RT)-PCR method
Arr10 arr12 double mutants showed relatively unchanged expression levels of ARR5, ARR6, and ARR7 and displayed highly reduced levels of ARR15 expression. Expression of these ARRs in arr1 arr10 arr12 triple mutants was completely unresponsive to cold. These results indicate that ARR1 is primarily involved in mediating cold signal for expressing type A ARRs and that ARR10 and ARR12 play some additive roles in this cold response

Summary

Introduction

The Arabidopsis (Arabidopsis thaliana) two-component signaling system, which is composed of sensor histidine kinases, histidine phosphotransfer proteins, and response regulators, mediates the cytokinin response and various other plant responses. We have previously shown that ARABIDOPSIS HISTIDINE KINASE2 (AHK2), AHK3, and cold-inducible type A ARABIDOPSIS RESPONSE REGULATORS (ARRs) play roles in cold signaling. Transgenic Arabidopsis expressing ARR1DDDK:GR lacking the amino-terminal receiver domain showed wild-type expression levels of type A ARRs in response to cold, indicating that the signal receiver domain of ARR1 might be important for cold-responsive expression of type A ARRs. ahp ahp ahp triple mutations greatly reduced type A ARR expression in response to cold, whereas the single or double ahp mutants displayed wild-type levels of ARR expression, suggesting that AHP2, AHP3, and AHP5 are redundantly involved in cold signaling Taken together, these results suggest that ARR1 mediates cold signal via AHP2, AHP3, or AHP5 from AHK2 and AHK3 to express type A ARRs. We further identified a cold transcriptome affected by ahk ahk mutations by microarray analysis, revealing a new cold-responsive gene network regulated downstream of AHK2 and AHK3. Cytokinin signaling of Arabidopsis (Arabidopsis thaliana) utilizes a multistep phosphorelay composed of sensor His kinases, His phosphotransfer proteins, and response regulators similar to the two-component signaling system of bacterial and yeast cells (To and Kieber, 2008). Microarray analysis of the Arabidopsis cold transcriptome affected by ahk ahk mutations compared with the wild type suggested that a new coldregulatory gene network exists downstream of AHK2 and AHK3

Methods

Results

Conclusion