15th International Conference on Arabidopsis Research - TAIR

T01-029
Molecular mechanism of floral repression during
vegetative development
Myriam Calonje(1), Lingjing Chen(1), Z. Renee Sung(1)
1-UC Berkeley
Flowering time in higher plants is finely regulated by floral inducers and floral
repressors. Recent investigations of early flowering mutants in Arabidopsis
reveal a variety of mechanisms by which flowering can be delayed and vegetative
growth extended (Sung et al., 2003). While some early flowering genes
interfere with the signaling process or inhibit the expression of floral inducer,
other genes such as CURLY LEAF (CLF) and EMBRYONIC FLOWER (EMF)
genes probably delay flowering by repressing the flower organ identity genes.
CLF and EMF2 encode Polycomb Group (PcG) proteins. In animals, PcG
proteins repress their target genes by modifying histone tails through deacetylation
and methylation, generating a PcG-specific histone code that recruits
other chromatin remodeling proteins to establish a stable, heritable mechanism
of epigenetic expression control. Owing to their conserved structural
and functional relationship to animal PcG proteins, plant PcG proteins might
function through a similar biochemical mechanism. PcG proteins control
multiple aspects of Arabidopsis development. The PcG target genes that have
been identified so far encode MADS box proteins. The deregulated expression
of ten MADS Box genes, such as, AG, AP3 and PI in emf mutants suggests
that these genes might be directly regulated by EMF2 PcG complex (Moon
et al., 2003). To investigate this possibility, we are performing Chromatin
Immunoprecipitation (ChIP) analysis on nuclear extracts from Arabidopsis
WT and emf2 mutant seedling using anti-EMF2 antiserum. Different regions
of the AP3 and PI promoters and of the AG second intron were analyzed
by PCR following the immunoprecipitations. The results are consistent with
hypothesis that EMF2 protein complex maintain the repression of the MADS
box genes in Arabidopsis vegetative development.
Moon et al., 2003. Plant Cell, 15(3):681-93.
Sung et al., 2003. Current Opinion in Plant Biology 6:29-35.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T01-030
Overexpression of KNAT1 interferes with Arabidopsis
ovule development
Elisabeth B. Truernit(1), James P. Haseloff(1)
1-Department of Plant Sciences, University of Cambridge, Downing Site, Cambridge CB2 3EA
The ovule is the female reproductive organ of higher plants. During Arabidopsis
thaliana ovule development two integuments grow out from the chalaza,
enclose the embryo and eventually develop into the seed coat (1). Cell division
and elongation in the ovule integuments need to be precisely and locally
regulated to achieve full enclosure of the plant embryo.
With the ultimate goal of identifying the factors that regulate integument
morphogenesis, we started to analyse aspects of outer ovule integument
development. Cell divisions in the outer integument were mapped and the
cellular events that lead to the development of highly specialized seed coat
cells (2) were monitored using fluorescent intracellular markers. Moreover,
Arabidopsis enhancer-trap lines were used to map domains of gene expression
during integument development and will be used to identify genes that are
expressed in this tissue.
The Arabidopsis outer ovule integument initially consists of two cell layers.
Overexpression of the homeodomain protein KNAT1 increases the number
of cell divisions specifically in the outer layer of the outer integument. Enhancer-trap
lines showing expression in specific domains of the outer integument
were crossed into KNAT1 overexpressing plants and were used as markers to
further characterize the effect of KNAT1 expression on integument development.
The down-regulation of a marker that was specifically expressed in the
outer layer of the outer integument suggests that KNAT1 interferes with outer
layer cell identity.
(1) Schneitz, Curr. Op. Plant Biol. (1999), 2:13 ¯ 17
(2) Windsor et al., Plant Journal (2000): 22:483-493
T01 Development 1 (Flower, Fertilization, Fruit, Seed)