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Plant and Cell Physiology Advance Access originally published online on July 10, 2007
Plant and Cell Physiology 2007 48(8):1192-1206; doi:10.1093/pcp/pcm089
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Overexpression of TaVRN1 in Arabidopsis Promotes Early Flowering and Alters Development

Hélène Adam, François Ouellet, Ndjido A. Kane, Zahra Agharbaoui, Geneviève Major, Yoko Tominaga and Fathey Sarhan*

Université du Québec à Montréal, Département des Sciences biologiques, Case Postale 8888, Succursale Centre-ville, Montréal, Québec, Canada H3C 3P8

*Corresponding author: E-mail, sarhan.fathey{at}uqam.ca; Fax, +1-514-987-4647.


  Abstract

TaVRN1, a member of the APETALA1 (AP1) subfamily of MADS-box transcription factors, is a key gene that controls transition from vegetative to reproductive phase in wheat. The accumulation of TaVRN1 transcripts in winter wheat probably requires the down-regulation of TaVRT2, a MADS-box factor that binds and represses the TaVRN1 promoter, and of the flowering repressor TaVRN2. However, the molecular mechanisms by which TaVRN1 functions as an activator of phase transition is unknown. To address this, a combination of gene expression and functional studies was used. RNA in situ hybridization studies showed that TaVRN1 transcripts accumulate in all meristems and primordia associated with flower development. An interaction screen in yeast revealed that TaVRN1 interacts with several proteins involved in different processes of plant development such as transcription factors, kinases and a cyclophilin. Arabidopsis plants overexpressing TaVRN1 flower early and show various levels of modified plant architecture. The ectopic expression causes an overexpression of the AP1 and MAX4 genes, which are associated with flowering and auxin regulation, respectively. The induction of gene expression probably results from the binding of TaVRN1 to CArG motifs present on the AP1 and MAX4 promoters. In contrast, Arabidopsis plants that overexpress TaVRT2, which encodes a putative flowering repressor, show an opposite late flowering phenotype. Together, the data provide molecular evidence that TaVRN1 may have pleiotropic effects in various processes such as control of axillary bud growth, transition to flowering and development of floral organs.

Keywords: Arabidopsis - Development - Flowering - MADS-box - Vernalization - Wheat

Abbreviations: bHLH, basic helix–loop–helix; EMSA, electrophoretic mobility shift assay; GUS, ß-glucuronidase; RLK, receptor-like kinase; RRM, RNA recognition motif; RT–PCR, reverse transcription–PCR; SAM, shoot apical meristem

(Received April 28, 2007; Accepted July 5, 2007)
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