15th International Conference on Arabidopsis Research - TAIR

T01-099
Graft transmission of floral signalling in Arabidopsis
is dependent on long-distance action of genes in the
photoperiod pathway
Colin Turnbull(1), Samuel Justin(1)
1-Department of Agricultural Sciences, Imperial College London, Wye Campus, Wye, Kent TN25
5AH, UK.
Photoperiodic regulation of flowering requires light perception in leaves,
followed by transmission of mobile ‘florigen’ signals from leaf to shoot apex.
However, no universal florigens have been discovered, and the genetics of
florigen signalling is largely unknown except in pea where several mutations
are associated with graft-transmissible positive or negative effects on flowering.
Using Arabidopsis micrografting (1), we demonstrate that certain flowering
time mutants can be rescued by long-distance signalling. Experiments
with [14C]sucrose showed that two-shoot ‘Y-grafted’ wild-type plants had
effective phloem continuity. If one of the grafted shoots was held in long days
(LD), it accelerated flowering of the second shoot which received only short
days, indicating that the LD signal is probably a positive regulator. We then
grafted wild-type plants to late-flowering, photoperiod-insensitive gi-2, co-2
or ft-7 mutants held under LD. Flowering times of gi-2 and co-2 were dramatically
accelerated relative to ungrafted controls, but a much smaller effect
was seen with ft-7. We conclude that native GI, CO and probably FT genes
can act in the leaf upstream of florigen signal generation. This is consistent
with recently published work showing that phloem-specific over-expression
of CO or FT was sufficient to rescue flowering time in corresponding mutant
backgrounds (2). The partial rescue of grafted ft-7 shoots may be explained
by the possible requirement of FT to be expressed in apex and leaf. Finally
we discuss analytical approaches to discovering the nature of the signal(s)
regulated by CO and/or its downstream target genes.
(1) Turnbull et al. (2002) Plant Journal 32, 255-262. (2) An et al. (2004) Development in press.
T01 Development 1 (Flower, Fertilization, Fruit, Seed)
T01-100
The Genetic and Molecular Network of SOC1 for
Flowering in Arabidopsis
Horim Lee(1), Jihyun Moon(1), Ilha Lee(1, 2)
1-School of Biological Sciences, Seoul National University, Seoul 151-742, Korea
Flowering is regulated by integrated network of several genetic pathways in
Arabidopsis. The key genes integrating multiple flowering pathways are FT,
SOC1 and LFY. To elucidate the interactions among them, genetic analyses
were performed using both loss-of-function mutants and gain-of-function
transgenics of the three integrators. Double mutant analysis showed that
SOC1 acts partially independently of FT for determination of flowering
time and acts in parallel with LFY for floral initiation, suggesting the three
integrators have both overlapping and independent functions. Furthermore,
the expression analysis showed that FT regulates the SOC1 expression, and
SOC1 regulates the LFY expression but not vice versa, which is consistent
with the fact that FT and LFY have the least overlapping functions among
the three integrators. The two integrators FT and SOC1 share a common
upstream negative regulator FLC, a flowering repressor integrating vernalization
and autonomous pathways. The flowering of ft soc1 is further delayed
by an increase of FLC expression, showing additional targets are regulated
by FLC. In addition, vernalization caused acceleration of flowering in the flc ft
soc1 triple mutant, suggesting that the vernalization pathway also has targets
other than FLC, FT, and SOC1. Finally, the triple mutant of ft soc1 lfy failed
to produce flowers and the triple overexpression of FT, SOC1, LFY caused
flowering right after germination with only two cauline leaves, which is very
similar to the phenotype of the embryonic flower mutant. This result suggests
that the integrative function of FT, SOC1, LFY are necessary and sufficient for
flowering.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin