Plant and Cell Physiology Advance Access originally published online on January 3, 2007
Plant and Cell Physiology 2007 48(2):263-277; doi:10.1093/pcp/pcl063
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ARR1 Directly Activates Cytokinin Response Genes that Encode Proteins with Diverse Regulatory Functions
1Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011 Japan
2MesengerScape Co., Ltd, Hatagaya 3-20-2, TS Bldg.-101 Shibuya-ku, Tokyo, 151-0072 Japan
*Corresponding author: E-mail, aoyama{at}scl.kyoto-u.ac.jp; Fax, +81-774-38-3259.
| Abstract |
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Plant cells respond to cytokinins by changing their gene expression patterns. The histidylaspartyl (HisAsp) phosphorelay mediates the signal from cytokinin receptors to type-B response regulators including ARR1, which transactivate cytokinin primary response genes. However, the overall architecture of the signal cascade leading to cytokinin-responsive phenomena is still unclear, mainly because it is not known how the HisAsp phosphorelay is connected to downstream phenomena. To reveal events immediately downstream from the phosphorelay-mediated transcriptional activation, we searched for direct-target genes of ARR1 by exploiting ARR1
DDKGR, a chimeric transcription factor that transactivates ARR1 direct-target genes in transgenic plants by glucocorticoid induction. We identified 23 direct-target genes, most of which were found to be cytokinin primary response genes. The arr1-1 mutation clearly affected the primary response in at least 17 genes, meaning that they respond primarily to cytokinins through the function of ARR1. The 17 genes encode proteins with diverse functions, including type-A response regulators, cytokinin metabolic enzymes and putative disease resistance response proteins. These results provide novel evidence indicating that the HisAsp phosphorelay is connected to diverse regulatory levels of cytokinin-responsive phenomena through ARR1 direct-target genes.
Keywords: Arabidopsis - ARR1 - Cytokinin - HiCEP - Phosphorelay - Target gene
Abbreviations: ARR, Arabidopsis response regulator; BA, benzyl adenine; CHX, cycloheximide; DEX, dexamethasone; DRRP, disease resistance response protein; GST, glutathione-S-transferase; HiCEP, high coverage expression profiling; HPt, histidine-containing phosphotransfer.
(Received November 11, 2006; Accepted December 21, 2006)
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