15th International Conference on Arabidopsis Research - TAIR

T01-079
Regulation of flowering time by gibberellins
Sven Eriksson(1), Henrik Böhlenius(1), Ove Nilsson(1)
1-Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish
University of Agricultural Sciences, S-901 83 Umeå, SWEDEN
In Arabidopsis, reduction in the level of active gibberellin (GA) delays
flowering in long days and prevents flowering in short days. The failure of
gibberellin-deficient ga1-3 mutants to flower under short-day conditions
is caused by a failure to upregulate the LEAFY promoter activity. We have
shown that GA4 is the active gibberellin responsible for LEAFY regulation
and that floral initiation under non-inductive short day conditions is preceded
by a dramatic increase in the shoot apical content of GA4 and sucrose. We
have also in detail analyzed the regulation of LEAFY by GA4. RT-PCR analysis
reveals that GA4 addition up-regulates LEAFY transcription very rapidly
and that the activation occurs in the presence of the translational inhibitor
cycloheximide, suggesting that the GA regulation of LEAFY transcription does
not require translation. Surprisingly, the translational inhibitors Cycloheximide,
Anisomycin, Emetine and Verrucarin A alone were able to superinduce
LEAFY expression. This effect is, at least partly, dependent on the activity of
the proteasome, indicating that LEAFY is under control of a labile repressor.
Furthermore, among many tested genes involved in flowering time regulation,
this effect appears to be specific to LEAFY. Finally, we have also characterized
the genetic interactions among various late flowering mutants and plants
with a constitutive GA response. This analysis has revealed new interactions
between the GA pathway and the long-day and autonomous pathways
controlling flowering time.
T01 Development 1 (Flower, Fertilization, Fruit, Seed)
T01-080
Identification of enhancers of elf3-7 through
activation tagging
Karen A. Hicks(1), Amy E. Aloe(1), Adam J. Booth(1)
1-Biology Department, Kenyon College
The control of floral initiation in Arabidopsis thaliana is regulated in part by
photoperiod, and a number of components in this pathway have been identified
through mutagenesis screens, including EARLY FLOWERING 3. ELF3 is
necessary for proper photoperiodic control of flowering and photomorphogenesis,
and may gate light input to the circadian oscillator. In order to identify
new components of the photoperiodic floral induction pathway, we have
performed an activation tagging screen in the elf3-7 mutant background.
While elf3-1 null alleles exhibit photoperiod-insensitive early flowering and
increased hypocotyl elongation, elf3-7 alleles exhibit early flowering and
increased hypocotyl elongation, but maintain photoperiod sensitivity. We have
created a large screening population by Agrobacterium-mediated transformation
of elf3-7 mutant plants, and have screened for T-DNA transformants that
show earlier flowering in non-inductive short day conditions, or enhancement
of the elf3-7 phenotype. Thus far, we have identified 18 transgenic lines with
alterations in flowering time, and our preliminary results suggest that these
phenotypes are heritable. In the future, we will further characterize these
mutant lines and identify genes whose increased expression results in the
phenotypes we observe.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin