First published online March 31, 2006; 10.1104/pp.106.076760
Plant Physiology 141:498-507 (2006)
© 2006 American Society of Plant Biologists
Regulation of Flowering in the Long-Day Grass Lolium temulentum by Gibberellins and the FLOWERING LOCUS T Gene
Rod W. King*,
Thomas Moritz,
Lloyd T. Evans,
Jerome Martin1,
Claus H. Andersen2,
Cheryl Blundell,
Igor Kardailsky and
Peter M. Chandler
Commonwealth Scientific and Industrial Research Organization, Plant Industry, Canberra, Australian Capital Territory 2601, Australia (R.W.K., L.T.E., C.B., P.M.C.); Swedish University of Agricultural Sciences, Umeå Plant Science Centre, S–901 83 Umea, Sweden (T.M.); DLF-Trifolium A/S, Research Division, DK–4660 Roskilde, Denmark (J.M., C.H.A.); and AgResearch, Grasslands Forage Biotechnology, Palmerston North, New Zealand (I.K.)
Seasonal control of flowering often involves leaf sensing of daylength coupled to time measurement and generation and transport of florigenic signals to the shoot apex. We show that transmitted signals in the grass Lolium temulentum may include gibberellins (GAs) and the FLOWERING LOCUS T (FT) gene. Within 2 h of starting a florally inductive long day (LD), expression of a 20-oxidase GA biosynthetic gene increases in the leaf; its product, GA20, then increases 5.7-fold versus short day; its substrate, GA19, decreases equivalently; and a bioactive product, GA5, increases 4-fold. A link between flowering, LD, GAs, and GA biosynthesis is shown in three ways: (1) applied GA19 became florigenic on exposure to LD; (2) expression of LtGA20ox1, an important GA biosynthetic gene, increased in a florally effective LD involving incandescent lamps, but not with noninductive fluorescent lamps; and (3) paclobutrazol, an inhibitor of an early step of GA biosynthesis, blocked flowering, but only if applied before the LD. Expression studies of a 2-oxidase catabolic gene showed no changes favoring a GA increase. Thus, the early LD increase in leaf GA5 biosynthesis, coupled with subsequent doubling in GA5 content at the shoot apex, provides a substantial trail of evidence for GA5 as a LD florigen. LD signaling may also involve transport of FT mRNA or protein because expression of LtFT and LtCONSTANS increased rapidly, substantially (>80-fold for FT), and independently of GA. However, because a LD from fluorescent lamps induced LtFT expression but not flowering, the nature of the light response of FT requires clarification.
1 Present address: Institut de Recherche pour le Développement, Unité Mixte de Recherche 5096 Laboratoire Génome et Développement des Plantes, 911 Avenue Agropolis, BP 64501, 34394 Montpellier cedex 5, France.
2 Present address: Plant Biotech Denmark, c/o the Royal Veterinary and Agricultural University, Department of Plant Biology, 40 Thorvaldsensvej, DK–1871 Frederiksberg C, Denmark.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Rod W. King (rod.king{at}csiro.au).
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.076760.
* Corresponding author; e-mail rod.king{at}csiro.au; fax 61–262465000.
Received January 29, 2006;
returned for revision March 16, 2006;
accepted March 21, 2006.
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