Genome-wide expression profiling of ARABIDOPSIS RESPONSE REGULATOR 7(ARR7) overexpression in cytokinin response

Abstract

The type-A ARRs of cytokinin two-component signaling system act as negative regulators for cytokinin signaling except for ARR4, but the molecular mechanism by which the A-type ARRs regulate cytokinin signaling remain elusive. To get insights into the molecular function of A-type ARR in cytokinin response, we sought to find the components that function downstream of A-type ARR protein by investigating the effects of ARR7 overexpression on cytokinin-regulated gene expression with the Affymetrix full genome array. To examine early cytokinin response, plants were treated with cytokinin for 30 min or 2 h, followed by GeneChip analysis. The hierarchical clustering analysis of our GeneChip data showed that ARR7 overexpression had distinctively repressive impacts on various groups of the cytokinin-regulated genes. In particular, the induction of all A-type ARRs except for ARR22, and AHK(ARABIDOPSIS HISTIDINE KINASE)1 and AHK4 was suppressed by ARR7. Cytokinin-induced expression of most of 12 expansin genes were repressed by ARR7, indicating potential involvement of ARR7 in cell expansion and plant development. Up-regulation of five cytokinin oxidase genes by cytokinins was negatively affected by ARR7. Our GeneChip analysis suggest that ARR7 mainly acts as a transcriptional repressor for a variety of early cytokinin-regulated genes encoding transcription factors, signal transmitters, plant development, and cellular metabolism, which may be responsible for reduced sensitivity of Arabidopsis transgenic plants overexpressing ARR7 to exogenous cytokinins.

A Subset of Cytokinin Two-component Signaling System Plays a Role in Cold Temperature Stress Response in Arabidopsis

“…7B). The weaker effects might be attributable to the lower ARR7 activity of these transgenic lines compared with line 4-11 with regard to the repression of its target genes, as reported previously (29). Cold treatment for 2 days efficiently induced a variety of coldregulated genes in the CBF/DREB pathway of both Pro 35S :ARR7 and control plants (Fig.…”

“…However, significantly enhanced freezing tolerance in ARR7 overexpression lines was found as compared with the arr7 mutants upon cytokinin preincubation. ARR7 overexpression caused insensitive cytokinin response similar to other A-type ARR genes (29). ARR7 overexpression in Pro 35S : ARR7 might have then reduced the effects of cytokinin exogenously applied by cytokinin preincubation.…”

“…ARRs might perform a function in stress tolerance response, we conducted electrolyte leakage assays for transgenic Arabidopsis overexpressing ARR7 (Pro 35S :ARR7) (29). Under normal conditions, Pro 35S :ARR7 (line 4-11) and both control plants, Pro 35S : GUS and the wild type (Col-0), showed similar ion leakage patterns (Fig.…”

“…12, C and D). As overexpression of ARR7 in Arabidopsis reduces response to cytokinin (29), this result might indicate that proper levels of cytokinin signaling might be important for cold tolerance.…”

“…The majority of A-type ARRs are partially redundant negative regulators of cytokinin signaling (28). The genome-wide expression profiling analysis of cytokinin response in the ARR7 overexpressor compared with the wild type demonstrated that ARR7 acts principally as a transcriptional repressor of a variety of early cytokinin-regulated genes encoding transcription factors, signal transmitters, plant development, and cellular metabolism (29). The Asp-85 mutation of ARR7 into the Asp residue blocked the phosphorylation of ARR7 by the Arabidopsis protein extracts in vitro and abolished the ability of ARR7 to suppress cytokinin-mediated responses in transgenic Arabidopsis (30), suggesting that the phosphorylation of ARR7 is essential to its function as a negative regulator of cytokinin signaling in Arabidopsis.…”