Plant Physiology Preview
Published on March 31, 2006; 10.1104/pp.106.076760
Received January 29, 2006
Returned for revision March 4, 2006
Accepted March 21, 2006
Regulation of flowering in the long day grass, Lolium temulentum L., by gibberellins and the gene, FLOWERING LOCUS T (FT)
Rod W. King *, Thomas Moritz , Lloyd T. Evans , Jerome Martin , Claus H. Andersen , Cheryl Blundell , Igor Kardailsky , and Peter M Chandler
CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia
Swedish University of Agricultural Sciences, Umeå Plant Science Centre, S-901 83 Umeå, Sweden
DLF-Trifolium A/S, Research Division, Hoejerupvej 31, DK-4660, Denmark
AgResearch, Grasslands Forage Biotechnology, Tennent Drive, Private bag 11008, Palmerston North, New Zealand
* Corresponding author; email: rod.king{at}csiro.au.
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 L may include gibberellins (GAs) and the gene FT. 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 increasing 5.7-fold vs. short day (SD), its substrate, GA19, decreasing equivalently and GA5, a bioactive product, increases 4-fold. A link between flowering, LD, GAs and GA biosynthesis is shown in three ways: (i) applied GA19 became florigenic on exposure to LD; (ii) expression of LtGA20ox1, an important GA biosynthetic gene, increased in a florally-effective LD involving incandescent lamps but not with non-inductive fluorescent lamps; (iii) Paclobutrazol (PAC), 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 favouring a GA increase. Thus, the early LD increase in leaf GA5 biosynthesis coupled with subsequent doubling in GA5 content at the shoot apex (King et al., 2001), provides a substantial trail of evidence for GA5 as a LD florigen. LD signalling may also involve transport of FT mRNA or protein as expression of LtFT and LtCONSTANS (CO) 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.
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