Plant and Cell Physiology Advance Access originally published online on July 16, 2008
Plant and Cell Physiology 2008 49(8):1237-1249; doi:10.1093/pcp/pcn100
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Structure and Functional Analysis of Wheat ICE (Inducer of CBF Expression) Genes
Département des Sciences Biologiques, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-ville, Montréal, Québec, Canada H3C 3P8
*Corresponding author: E-mail, houde.mario{at}uqam.ca; Fax, +81-514-987-4647.
| Abstract |
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Two different inducers of CBF expression (ICE1-like genes), TaICE41 and TaICE87, were isolated from a cDNA library prepared from cold-treated wheat aerial tissues. TaICE41 encodes a protein of 381 aa with a predicted MW of 39.5 kDa while TaICE87 encodes a protein of 443 aa with a predicted MW of 46.5 kDa. TaICE41 and TaICE87 share 46% identity while they share 50 and 47% identity with Arabidopsis AtICE1 respectively. Expression analysis revealed that mRNA accumulation was not altered by cold treatment suggesting that both genes are expressed constitutively. Gel mobility shift analysis showed that TaICE41 and TaICE87 bind to different MYC elements in the wheat TaCBFIVd-B9 promoter. Transient expression assays in Nicotiana benthamiana, showed that both TaICE proteins can activate TaCBFIVd-B9 transcription. The different affinities of TaICE41 and TaICE87 for MYC variants suggest that ICE binding specificity may be involved in the differential expression of wheat CBF genes. Furthermore, analysis of MYC elements demonstrates that a specific variant is present in the wheat CBF group IV that is associated with freezing tolerance. Overexpression of either TaICE41 or TaICE87 genes in Arabidopsis enhanced freezing tolerance only upon cold acclimation suggesting that other factors induced by low temperature are required for their activity. The increased freezing tolerance in transgenic Arabidopsis is associated with a higher expression of the cold responsive activators AtCBF2, AtCBF3, and of several cold-regulated genes.
Keywords: Arabidopsis - DNA binding - Freezing tolerance - Promoter - Transcription factor - Transactivation
Abbreviations: AP2, Apetala2; bHLH, basic helix-loop-helix; CBF, C-repeat binding factor; CRT, C-repeat; CA, cold-acclimated; COR, cold-regulated; DRE, dehydration responsive element; DREB, drought responsive element binding; EMSA, electrophoretic mobility shift assay; EREBP, ethylene responsive element binding protein; ESTs, expressed sequenced tags; FT, freezing tolerance; GFP, green fluorescent protein; HOS1, high expression of osmotically responsive genes 1; ICE, inducer of CBF expression; LTREs, low-temperature-responsive elements; MYB15, Myb domain protein 15; NA, non-acclimated; WT, wild type.
1These authors contributed equally to this work.
(Received June 13, 2008; Accepted July 7, 2008)
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