Plant and Cell Physiology Advance Access originally published online on December 22, 2006
Plant and Cell Physiology 2007 48(2):205-220; doi:10.1093/pcp/pcl061
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Molecular Basis of Late-Flowering Phenotype Caused by Dominant Epi-Alleles of the FWA Locus in Arabidopsis
1Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan
2CREST, Japan Science and Technology Agency, Kawaguchi, 332-0012 Japan
3Adjunct Division of Applied Genetics, National Institute of Genetics, Mishima, 411-8540 Japan
*Corresponding author: E-mail, taraqui{at}lif.kyoto-u.ac.jp; Fax, +81-75-753-6470.
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Abstract |
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The late-flowering phenotype of dominant fwa mutants is caused by hypomethylation in the FWA locus leading to ectopic expression of a homeodomain leucine zipper (HD-ZIP) protein. However, little is known about whether FWA has any role in regulation of flowering and how ectopically expressed FWA delays flowering. Through analysis of FWA expression in wild-type seedlings, it was shown that FWA is not expressed during the vegetative phase. This suggests that FWA has no role in flowering. The previous reports that fwa suppressed the precocious-flowering phenotype of plants overexpressing FLOWERING LOCUS T (FT) suggest that the flowering pathway(s) either at and/or downstream of FT is blocked by FWA. Comparison of gene expression profiles in three genetic backgrounds ectopically expressing FWA and their respective wild types failed to detect common changes, ruling out the possibility that FWA acts through transcriptional misregulation. Yeast two-hybrid analysis and in vitro pull-down assay showed that FWA protein can specifically interact with FT protein. The importance of protein interaction with FT in delaying flowering was supported by studies involving N-terminal and C-terminal truncations of FWA. The C-terminal truncation with abolished interaction did not delay flowering when overexpressed, while the N-terminal truncation, which retains interaction, did. Specific interaction of FWA with FT enabled us to use FWA protein as a specific inhibitor of FT protein function. Through tissue-specific ectopic expression of FWA, further support for the shoot apex being the site of action of FT protein was provided.
Keywords: Arabidopsis - Epi-mutant - Flowering - FT - FWA - Protein interaction
Abbreviations: AD, Gal4 activation domain; BD, Gal4 DNA-binding domain; bZIP, basic region/leucine zipper; EMS, ethylmethane sulfonate; GST, glutathione S-transferase; GUS, ß-glucuronidase; HD, homeodomain; HD-ZIP, homeodomain leucine zipper; LD, long day; ORF, open reading frame; RT–PCR, reverse transcription–PCR; 35S, cauliflower mosaic virus 35S RNA promoter; SD, short day; SINE, short interspersed element; START, StAR-related lipid transfer protein domain; UTR, untranslated region; ZLZ, zipper–loop–zipper
4 Present address: Department of Molecular Biology, Max Planck Institute for Developmental Biology, D-72076 Tübingen, Germany.
5 Present address: Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan.
(Received November 25, 2006; Accepted December 15, 2006)
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