15th International Conference on Arabidopsis Research - TAIR

T01-063
Control of Arabidopsis petal size by a novel RING
finger protein
Sabine Disch(1), Jennifer C. Fletcher(2), Michael Lenhard(1)
1-Institut für Biologie III, Universität Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany
2-USDA/UC Berkeley, Plant Gene Expression Center, Albany, CA 94710, USA
The species-specific size of plant organs is under tight
genetic control as evidenced by the very low variability in
size when genetically identical individuals are grown under
the same environmental conditions. However, the genetic and
molecular basis of organ size control in plants is largely
unknown.
To begin to dissect the underlying regulatory mechanisms,
we are characterizing a novel Arabidopsis mutant, big
brother2 (bb2), that shows a dramatic overgrowth of petals
and to a lesser extent of sepals and the stem. This appears
to be due to an extended period of growth, rather than to
faster growth. The enlargement of petals is independent of
the known growth promoter AINTEGUMENTA (1), suggesting that
bb2 defines a novel regulatory pathway in growth control.
The phenotype is due to the deletion of an uncharacterized
gene encoding a protein with a RING-finger domain.
Intriguingly, heterozygous bb2 mutants also show an
intermediate enlargement of organs, suggesting that BB2
regulates organ growth in a dosage-dependent manner.
(1) Mizukami and Fisher (2000), PNAS 97, 942-947
T01 Development 1 (Flower, Fertilization, Fruit, Seed)
T01-064
Functional analysis of armadillo repeat-only (ARO)
proteins in Arabidopsis thaliana
M. Gebert(1), T. Dresselhaus(1), S. Sprunck(1)
1-Biocenter Klein Flottbek, Dept. Developmental Biology & Biotechnology, University of Hamburg,
Ohnhorststr.18, D-22609 Hamburg, Germany
The armadillo domain (Arm) was first identified in the Drosophila segment polaritiy
gene armadillo. It codes for beta-catenin, wich functions in cell to cell
adhesion but also as a component of the wnt-signalling pathway, regulating
cell fate and polarity. Proteins containing Arm repeats possess tandem copies
of a degenerated protein sequence motif of about 42 amino acids that form a
conserved three-dimensional structure mediating protein-protein interactions
[1]. Most of these proteins are involved in intracellular signalling or regulation
of gene expression during developmental processes. In contrast to animals,
only two Arm repeat containing proteins have been functionally characterized
in plants [2,3]. Nevertheless, 108 predicted Arm repeat proteins have been
identified in the Arabidopsis genome [4], which can be subdivided on the
base of their homology and the occurrence of additional motifs (e.g. U-box,
F-box, S/T kinase, etc). Besides those subfamilies containing defined motifs
of known function adjacent to the Arm domain, there is a subgroup of at least
26 Arm genes without any further known protein motif and with yet unknown
function (ARO). Three of these genes encode proteins with significant homology
to a wheat arm repeat protein from unfertilized egg cells. The wheat
homolog (TaAro1) shows female and male gametophyte-specific expression.
Likewise, one of the corresponding A. thaliana genes, AtAro1, can be detected
specifically in female and male gametophytic tissues of Arabidopsis by
RT-PCR studies. The other two genes (AtAro2 and AtAro3) are also expressed
in vegetative tissues. Promoter activity of AtAro1 was analyzed using GUS
as a reporter gene. Since database searches revealed the existance of a
putative transmembrane domain for AtAro1, subcellular localization of the
proteins was investigated using GFP fusion proteins in transient expression
studies. T-DNA insertion lines of all three genes are currently examined for
phenotypes, especially in respect to gametophyte formation and function.
Future studies include the ectopic overexpression af AtAro1 and a screening
for interacting proteins.
[1] Coates, J.C. (2003); [2] Stone, S.L. et al. (2003); [3] Amador V. et al. (2001) [4] Mudgil, Y. et
al. (2004)
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin