15th International Conference on Arabidopsis Research - TAIR

T01-043
Identifying downstream targets of INDEHISCENT
(IND), a bHLH transcription factor important for fruit
dehiscence
Kristina Gremski(1), Pedro Robles(1, 2), Martin F. Yanofsky(1)
1-Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093-0116,
USA
2-Division de Genetica and Instituto de Bioingenieria, Universidad Miguel Hernandez, Campus de
Elche, 03202 Elche, Alicante, Spain
Arabidopsis has dry fruits that open to release their seeds through a process
known as dehiscence. When the fruits are mature, the seed pod walls, or
valves, separate from the central replum at the valve margins. The valve
margins are composed of specialized cells that undergo cell-cell separation
during dehiscence. Several genes that are important for valve margin
differentiation have been characterized. One of these genes is INDEHIS-
CENT (IND), which encodes a basic helix-loop-helix transcription factor. We
are interested in identifying the downstream targets of IND and eventually
unraveling the entire cascade of gene activity that leads to valve margin
differentiation and fruit dehiscence. To this end we have created an inducible
IND overexpression line with IND fused to the glucocorticoid receptor (GR).
We are planning to use the Affymetrix microarrays to identify genes that are
differentially expressed due to IND induction and due to loss of IND activity.
Preliminary results from microarrays comparing the ind mutant to wild type
will be presented.
Liljegren et al. (2004) Cell 116(6):843-53
T01 Development 1 (Flower, Fertilization, Fruit, Seed)
T01-044
Moleculer Basis of Late-Flowering Phenotype in
Dominant fwa Mutants
Yoko Ikeda(1), Mitsutomo Abe(1, 2), Takashi Araki(1, 3)
1-Department of Botany, Graduate School of Science, Kyoto University
2-Bio-oriented Technology Research Advancement Institution, Japan
3-CREST, Japan Science and Technology Agency
Dominant late-flowering mutant fwa is an epigenetic mutant that ectopically
expresses a GL2-class HD-ZIP gene due to promoter hypomethylation (Soppe
et al. 2000). In wild type, however, FWA is not expressed during vegetative
phase, and loss-of-function mutants of FWA are indistinguishable from wild
type in flowering time. These facts suggest that FWA per se is not a component
of the regulatory mechanisms of flowering. Genetic analysis suggests
that FWA blocks the pathway at FT and/or downstream of FT. We envisage
that FWA may provide a unique tool to dissect pathway from FT to flowering.
We examined interaction of FWA protein with known flowering regulators
such as FT, TFL1 and FD. FWA protein strongly interacted with FT protein
through its C-terminal region and ZIP domain in yeast cells. No interaction
was observed between FWA and TFL1 or FWA and FD. Interaction between
FWA and FT was confirmed by the in vitro pull down assay. C-terminal
truncation of FWA abolished interaction with FT. Overexpression of C-terminal
truncated FWA did not cause late-flowering phenotype. These suggest that
ectopically-expressed FWA inhibits floral transition by interfering with the FT
function through protein-protein interaction.We hypothesize that ectopic FWA
inhibits floral transition by interfering with the interaction between FT and a
meristem-specific bZIP transcription factor FD through binding to FT. To test
this, FWA is being expressed in various parts of plant to determine the tissue
where FWA can exert its negative effect on flowering.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin