15th International Conference on Arabidopsis Research - TAIR

T01-035
FIDGET (FIT), an APETALA2-like protein promotes
flowering by direct activation of FT
Stephan Wenkel(1), Lionel Gissot(1), Jose Gentilhomme(1), George Coupland(1)
1-Max-Planck-Institute for Plant Breeding Research, Carl-von-Linne Weg 10, 50829 Koeln,
Germany
Arabidopsis thaliana is a facultative long-day plant, flowering earlier under
long than short-day conditions. CONSTANS, a central protein in the photoperiod
response pathway, promotes flowering by activating transcription of FT
under long days. The induction of FT leads to the transcription of the floral
meristem identity genes LFY and AP1. So far, CO is the only protein described
to activate FT expression and thereby induce early flowering in long days.
We have successfully used the yeast-one-hybrid technology to identify
new proteins interacting with the promoter of FT. One of these proteins is
FIDGET (FIT), which interacted with a 300 bp-fragment of the FT-promoter in
yeast and in vitro. FIT is an AP2-like protein that belongs to the subclass of
ethylene-responsive element binding proteins (EREBP). FIT mRNA shows a
circadian expression pattern peaking 16 hours after dawn.
In transient promoter studies we found that FIT is able to activate the
expression of FT. Overexpression of FIT from the 35S promoter produced
slightly earlier flowering plants, but expression from the SUC2-promoter in
the phloem companion cells, where FT is thought to act, results in a clearly
early-flowering phenotype. The expression pattern of FIT is being analyzed
using promoter-GUS fusions and SUC2::FIT is being crossed into various
flowering-time mutants to place it within the current model of the network of
genes that control flowering in Arabidopsis.
T01 Development 1 (Flower, Fertilization, Fruit, Seed)
T01-036
Inhibition of the V-ATPase leads to deformation of
golgi stacks during male gametophyte development
Jan Dettmer(1), York D. Stierhof(2), Renate Schmidt(3), Karin Schumacher(1)
1-ZMBP, Pflanzenphysiologie , Universität Tübingen, 72076 Tübingen, Germany
2-ZMBP, Mikroskopie, Universität Tübingen, 72076 Tübingen, Germany
3-Max-Planck-Institut für Molekulare Pflanzenphysiologie, 14476 Golm, Germany
The V-ATPase is a highly conserved eukaryotic proton pump, which uses ATP
to pump H+ from the cytosol into the lumen of different intracellular compartments.
Acidification of endomembrane compartments and consequently the
establishment of a proton gradient is important for various cellular functions
such as secondary active transport, enzyme function, protein targeting, and
vesicle trafficking.
In order to analyze V-ATPase function in vivo, we identified T-DNA insertions
disrupting genes encoding Arabidopsis V-ATPase subunits. A T-DNA insertion
in the single copy gene encoding the catalytic subunit VHA-A showed a severely
reduced transmission rate and we failed to identify plants homozygous
for this insertion. Reciprocal crosses showed that inactivation of the catalytic
subunit leads to complete male and partial female sterility. Complementation
of the vha-A allele rescued the sterility phenotype. Tetrad analysis of pollen
from vha-A/+ plants combined with electron microscopy revealed, that the
first visible result of a lack of V-ATPase activity was a deformation of golgi
stacks. The observed cell death of two pollen per tetrad in later stages might
be a result of this golgi abnormality. The importance of the V-ATPase for the
functionality of the golgi apparatus was further confirmed by pharmacological
studies using Concanamycin A, a specific inhibitor of the V-ATPase.
Treatment of growing pollen tubes with Concanamycin A led to a reduction of
polar cell elongation and electron microscopy showed similar deformations of
golgi stacks as seen in the vha-A pollen.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin