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The HDZip Class I Transcription Factors in Arabidopsis thaliana: Characterisation of HDZip Genes Involved in the Mediation of Environmental Signals
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Physiological Botany.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Homeodomain leucine zipper (HDZip) proteins constitute a large family of transcription factors characterised by the presence of a DNA-binding homeodomain and an adjacent leucine zipper motif, which mediates protein-dimer formation. The HDZip genes of Arabidopsis have been divided into four classes, HDZip I-IV. This thesis describes the characterisation and phylogeny of the class I HDZip genes and focuses on the expression and function of four HDZip I genes, ATHB5, -6, -7 and -16.

The phylogenetic analyses of the 17 HDZip I sequences defined six subclasses, supported by the intron patterning and the traced duplication history of the genes. The members within each subclass showed diversification in expression, suggesting that the cis regulatory regions of the closely related genes have undergone evolutionary changes. However, similarities in the gene expression patterns between genes also exist and external factors like the availability of water and quality of light directs the expression of a subset of HDZip I genes. Expression analyses revealed that the plant hormone abscisic acid (ABA) is involved as a systemic signal for the salt or osmoticum induced ATHB7 expression, whereas light signals mediated through the blue light photoreceptors was found to direct the expression of ATHB6.

Phenotypic analyses of plants with altered levels of ATHB6 or ATHB16 suggested that these paralogous genes encode proteins with very similar functions. ATHB16 was shown to act as a negative regulator of leaf cell expansion, as a suppressor of the flowering time sensitivity to photoperiod and as a positive regulator of blue light dependent inhibition of hypocotyl growth. A similar role for ATHB6 in the regulation of hypocotyl elongation was recorded. Further, analyses of multiple loss-of-function plants demonstrated that ATHB5, -6 and -16 function at least in part redundantly in mediating light effects on hypocotyl elongation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2004. , p. 53
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1003
Keywords [en]
Plant physiology
Keywords [sv]
Växtfysiologi
National Category
Botany
Identifiers
URN: urn:nbn:se:uu:diva-4507ISBN: 91-554-6018-6 (print)OAI: oai:DiVA.org:uu-4507DiVA, id: diva2:164971
Public defence
2004-09-24, Lecture hall, room 3041, Department of Physiological Botany, Villavägen 6, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2009-04-02Bibliographically approved
List of papers
1. HDZip class I genes in Arabidopsis: expression profiles and phylogenetic relationships
Open this publication in new window or tab >>HDZip class I genes in Arabidopsis: expression profiles and phylogenetic relationships
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(English)Manuscript (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:uu:diva-92027 (URN)
Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2010-01-14Bibliographically approved
2. Salt stress signalling and the role of calcium in the regulation of the Arabidopsis ATHB7 gene
Open this publication in new window or tab >>Salt stress signalling and the role of calcium in the regulation of the Arabidopsis ATHB7 gene
2005 (English)In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 28, no 2, p. 202-210Article in journal (Refereed) Published
Abstract [en]

In plants changes in cytosolic calcium ion concentrations ([Ca2+]cyt) have been detected after various stress treatments, including salt treatment. The involvement of a Ca2+ signal as an essential component of signalling pathways leading to downstream responses, such as gene expression, is supported only by a few studies. In this study the possible involvement of the salt stress-induced increase in [Ca2+]cyt in the signalling pathway leading to the induction of ATHB7, a homeobox gene encoding a homeodomain leucine zipper (HDZip) transcription factor was analysed. The salt-induced expression of ATHB7 was found to be independent of the Ca2+ signal evoked by salt. Instead, it was found that ATHB7 expression in shoots was not dependent on a direct contact with salt or osmoticum, whereas in roots, ATHB7 seemed to be induced by the direct contact, indicating that signals from roots cause systemic induction of ATHB7. Abscisic acid (ABA) or ABA-dependent components were found to, at least partly, to function as the systemic signal.

Keywords
aequorin, gene expression, HDZip, signal transduction
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-92028 (URN)10.1111/j.1365-3040.2004.01263.x (DOI)
Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2017-12-14Bibliographically approved
3. The Arabidopsis homeobox gene, ATHB16, regulates leaf development and the sensitivity to photoperiod in Arabidopsis
Open this publication in new window or tab >>The Arabidopsis homeobox gene, ATHB16, regulates leaf development and the sensitivity to photoperiod in Arabidopsis
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2003 (English)In: Developmental Biology, Vol. 264, p. 228-239Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92029 (URN)
Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2009-04-02Bibliographically approved
4. The HDZip class I genes ATHB5, -6 and -16 act redundantly to mediate light effects on hypocotyl elongation
Open this publication in new window or tab >>The HDZip class I genes ATHB5, -6 and -16 act redundantly to mediate light effects on hypocotyl elongation
Show others...
(English)Manuscript (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:uu:diva-92030 (URN)
Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2010-01-14Bibliographically approved

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