A paper by Blazquez et al. (2002) discusses the possible role
of the clock in the Gibberellin (GA) biosynthesis pathway.
toc1 mutation partially suppresses the ga1-3 phenotype:
Long Days (LD),
it accelerates flowering, and in Short Days (SD), it
restores the ability to flower. In both cases, the toc1 ga1-3
mutants flower just a bit later than toc1
mutants. In toc1 ga1-3 and toc1
mutants, LFY expression increases fast (although it does
not reach the levels it does in the WT prior to flowering).
This means that LFY expression is also regulated by a
mechanism independent of GAs (Blazquez
et al., 2002).
However, when the same experiment is performed in
21h-cycles, the partial suppression by toc1-1 of the
ga1-3 phenotype is not observed any more. As 21h is the
duration of the clock endogenous period in the
toc1-1 single mutant, this apparent suppression of the
ga1-3 phenotype could actually
be due only to the effects of TOC1 on the clock.
the expression profiles of flower integrators such as
CO, SOC1 and FT, are similar in the WT and
toc1-1 mutant in
LD and in 21h cycles, but not in SD (Blazquez
et al., 2002).
There is some
redundancy between the photoperiod and the GA
transduction pathways in LD:
The late-flowering mutant
phenotype of ga1-3 is enhanced in the double mutant
co-2 ga1-3: this mutant does not flower at all in
SD or in LD (Reeves and
Coupland, 2001; See also:
Putterill et al., 1995;
Michaels and Amasino, 1999).
Possible response of the GA biosynthesis pathway to
Besides being negatively regulated by the GAs, the
GA20ox (GA5) and GA3ox (GA4) transcripts are also regulated by the
light (Yamaguchi et al., 1998(2)). However,
it is not mentioned if these changes actually affect
the flowering time.
These observations could
actually be a consequence of the
between GI and SPY.
It is also documented that
light and photoperiod have an effect on GA biosynthesis
and response, for example in germination (Yamaguchi
et al., 1998). However, their
effect on flowering time is not as well documented (See
Kamiya and Garcia-Martinez, 1999).