LHY and CCA1 are clock components and
TFL1 encodes a shoot-identity gene in
Arabidopsis. When combined with
tfl1,
lhy cca1 results in precocious and ectopic expression of a floral integrator gene,
LFY. We have shown that
lhy cca1 and
GI-ox cause early flowering and increase the expression of two floral integrator genes,
FT and
SOC1.
FT and
SOC1 are required for the early flowering of
GI-ox under SD. Here we demonstrate that
tfl1 dramatically reduced the generation time of
GI-ox as well as
lhy cca1 plants.
tfl1 enhanced the precocious expression of the meristem-identity gene
AP1 in
GI-ox in a similar way to that in
lhy cca1. However,
tfl1 did not affect the mRNA levels of
FT and
SOC1 in
lhy cca1 and
GI-ox, suggesting that the additive phenotypes in
lhy cca1 tfl1 (and
GI-ox tfl1) are attributable to the concurrent up-regulation of three genes,
FT/SOC1 and
LFY. The terminal flower phenotype of
tfl1 was enhanced by
lhy cca1 and
GI-ox under SD, suggesting that a proper balance between FT and TFL1 with antagonistic roles is important for the photoperiodic control of architecture in
Arabidopsis. Our results indicate that GI mediates between the circadian clock and three floral integrator genes,
FT,
SOC1 and
LFY, to control the photoperiodic flowering.
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