JXB Advance Access published online on October 17, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern232
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
The nature of floral signals in Arabidopsis. II. Roles for FLOWERING LOCUS T (FT) and gibberellin
CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2600, Australia
To whom correspondence should be addressed. E-mail: rod.king{at}csiro.au
Signals produced in leaves are transported to the shoot apex where they cause flowering. Protein of the gene FLOWERING LOCUS T (FT) is probably a long day (LD) signal in Arabidopsis. In the companion paper, rapid LD increases in FT expression associated with flowering driven photosynthetically in red light were documented. In a far red (FR)-rich LD, along with FT there was a potential role for gibberellin (GA). Here, with the GA biosynthesis dwarf mutant ga1-3, GA4-treated plants flowered after 26 d in short days (SD) but untreated plants were still vegetative after 6 months. Not only was FT expression low in SD but applied GA bypassed some of the block to flowering in ft-1. On transfer to LD, ga1-3 only flowered when treated simultaneously with GA, and FT expression increased rapidly (<19.5 h) and dramatically (15-fold). In contrast, in the wild type in LD there was little requirement for GA for FT increase and flowering so its endogenous GA content was near to saturating. Despite this permissive role for endogenous GA in Columbia, RNA interference (RNAi) silencing of the GA biosynthesis gene, GA 20-OXIDASE2, revealed an additional, direct role for GA in LD. Flowering took twice as long after silencing the LD-regulated gene, GA 20-OXIDASE2. Such independent LD input by FT and GA reflects their non-sympatric expression (FT in the leaf blade and GA 20-OXIDASE2 in the petiole). Overall, FT acts as the main LD floral signal in Columbia and GA acts on flowering both via and independently of FT.
Key words: Arabidopsis, far-red light, flowering, FT, gibberellin, c long day.l
* Present address: National Institute of Floricultural Science (NIFS), Tsukuba, 305-8519 Japan
Received 9 June 2008; Revised 14 July 2008 Accepted 15 August 2008
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