75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

173 Flowering Time Control in Arabis alpina, a Perennial Relative of Arabidopsis thaliana
Renhou Wang 1 , Maria Albani 1 , Coral Vincent 1 , Franziska Turk 1 , Fabio Fornara 1 , Carlos Blanco 2 , George Coupland 1
1
Department of Plant Developmental Biology, Max-Planck-Institute for Plant Breeding Research, Koln,
Germany, 2 Departamento de Genetica Molecular de Plantas, Centro Nacional de Biotecnologia, CSIC, Madrid,
Spain
To study flowering-time control in polycarpic perennials and perennialism-related traits such as juvenility, we
have developed Arabis alpina as a model species. As a member of the Brassicacea family, A.alpina is closely related to
Arabidopsis thaliana, which makes it easy to transfer to Arabis alpina the knowledge on flowering acquired in Arabidopsis.
Arabis alpina has other important attributes that make it an attractive model species such as being diploid and able to
self fertilize.
We have investigated juvenility in Arabis alpina, a trait not shown by Arabidopsis. Arabis alpina has a four-weeklong
juvenile phase, during which the plant does not flower in response to floral inductive signals, such as vernalization
treatment, that are sufficient to cause adult plants to flower. To unravel the underlying mechanisms, homologues of
Arabidopsis flowering time and floral meristem identity genes, FLC, TFL1, FT, SOC1, and LFY have been isolated
from A.alpina and named AaFLC, AaTFL1, AaFT, AaSOC1, and AaLFY respectively. The expression patterns of these
genes were tested in juvenile and adult plants. The results suggest high levels of AaTFL1 in the meristems of juvenile
plants might correlate with juvenility.
Another interesting issue we are studying in A.alpina is the genetic basis of natural variation in flowering time of
different accessions. Two accessions with distinct vernalization requirements for flowering have been identified. The Pajares
accession has an obligate requirement for vernalization to promote the floral transition whereas the Bonn accession flowers
early without vernalization. Analysis of expression of different flowering-time genes showed that AaFLC was expressed
at similarly high levels in both accessions while homologues of the floral pathway integrator genes, AaFT and AaSOC1
were expressed at higher levels in the Bonn accession than in the Pajares one. Genetic analysis indicated that the distinct
vernalization requirements for flowering in these two Arabis alpina accessions mainly arise from a locus other than AaFLC
and the allelic variation at this locus does not affect AaFLC expression levels. This observation is in contrast to Arabidopsis
where most of the natural variation in vernalization is either at FLC or FRI, which regulates FLC expression.
174 A novel regulatory pathway that promotes flowering in response to UV light identified by
high-throughput misexpression of Arabidopsis transcription factors
Stephan Wenkel, Lionel Gissot, Jose Le Gourrierec, Aneta Domen, George Coupland
Max-Planck-Institute for Plant Breeding Research
In order to isolate novel transcription factors that are involved in controlling flowering in Arabidopsis, we performed
a large-scale misexpression screen. Around 1,000 Arabidopsis transcription factors were expressed under the SUC2-
promoter in the phloem companion cells, where CONSTANS (CO) and FLOWERING LOCUS T (FT) are expressed and
act to promote flowering. Screening of T1-transformants revealed several late and early flowering lines misexpressing
transcription factors that belong to different families. We misexpressed 69 APETALA2-LIKE transcription factors and
of these 62 had no effect on flowering time, four caused late flowering and three caused early flowering. In a parallel
approach we identified proteins that bind to the FT promoter by yeast-one-hybrid screening. One of the interacting proteins
was named FIDGET (FIT). FIT caused early flowering when expressed under the SUC2 promoter. The early flowering
phenotype of SUC2::FIT is caused by upregulation of FT. Furthermore, we demonstrate that FIT binds to the FT promoter
in yeast, in vitro and in vivo. We tested to which environmental cues FIT expression responds and found that it is highly
induced upon UV treatment. UV light also induces FT expression and accelerates flowering in an FT dependent manner.
Two other AP2-like transcription factors that caused late flowering can also interact with the FT promoter in yeast. This
suggests that UV as well as other stress-related pathways, involving AP2-like transcription factors, converge on the
control of FT expression to regulate flowering time in response to environmental stimuli.