15th International Conference on Arabidopsis Research - TAIR

T01-097
The Arabidopsis formin AtFH5 is a potential effector
of Polycomb group activity in endosperm polarity
Jonathan N. Fitz Gerald(1), Mathieu Ingouff(1), Christophe Guérin(2), Hélène
Robert(1), Mikael Blom Sørensen(1), Laurent Blanchoin(2), Frédéric Berger(1)
1-Laboratoire de Reproduction et Développement des Plantes, UMR 5667, Ecole Normale Supérieure
de Lyon, 46 Allée d'Italie, F-69364 Lyon, Cedex 07, France
2-Laboratoire de Physiologie Cellulaire Végétale, UMR 5168, DRDC, Commissariat à l'Energie
Atomique Grenoble, 17 rue des Martyrs, F-38054 Grenoble cedex 9, France
The Polycomb group (Pc-G) proteins are widely conserved transcriptional repressors.
They act as a modular complex that maintains expression patterns
epigenetically through chromatin remodeling. In Arabidopsis, mutations in
any of the three fertilization independent seed (FIS) Pc-G members result in
an aberrant endosperm development: over-proliferation of the endosperm
nuclei, enlargement of cysts in the posterior pole and an absence of the
developmental transition from syncytial to cellularized endosperm.
We have previously reported the characterization of an enhancer trap line,
KS117, whose GFP expression in the posterior pole is disrupted in a fis
background. The T-DNA responsible for KS117 expression was localized
to the formin coding gene AtFH5. Formins are actin nucleating agents
whose conserved function in cytokinesis and cell polarity makes them likely
candidates as targets of FIS pathways. in situ hybridization in the wild-type
seed revealed that AtFH5 expression is limited to the cyst and nodules of the
posterior endosperm. To test the biochemical function of the AtFH5 gene
product, actin assembly was characterized using a combination of fluorescence
spectroscopy and light microscopy. Purified recombinant AtFH5 was
able to nucleate and cap actin filaments in vitro. Finally, an AtFH5 insertion
line was identified that truncates the AtFH5 transcript within the conserved
Formin Homology 2 domain. These mutant atfh5 plants delay endosperm
cellularization. In addition, over 20% of atfh5 seeds lack posterior cyst
structures, suggesting a role for AtFH5 in nuclei migration to the posterior
pole. Thus, localization, activity and mutant phenotype are all consistent with
a model in which FIS activity promotes endosperm polarity by targeting the
Arabidopsis formin AtFH5 to the posterior pole.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T01-098
Establishment of fruit patterning in Arabidopsis
Jose R. Dinneny(1), Detlef Weigel(1), Martin F. Yanofsky(1)
1-Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA
2-Department of Molecular Biology, Max Planck Institute for Developmental Biology, D-72076
Tübingen, Germany
Determining the mechanisms that establish shape and identity in organs has
long been a goal for developmental biology. In plants, while many gains have
been made uncovering the genetic pathways that specify organ identity, little
is known about the downstream processes that actually regulate morphology
and cell type. Work focusing on the development of the Arabidopsis
fruit, however, has begun to elucidate some of these processes. The fruit is
composed of three domains, the valves, or seed pod walls, the replum which
develops in between the two valves, and the valve margin which develops
at the valve/replum border. Seed dispersal is promoted by the valve margin,
which undergoes a process of cell-cell separation that facilitates the detachment
of the valves from the replum. Valve margin formation is dependent
on the activation of the valve margin identity genes, SHATTERPROOF1,2,
ALCATRAZ and INDEHISCENT. In addition, the restricted activation of these
identity genes to the valve margin is controlled by the repressive activities
of FRUITFULL in the valves and REPLUMLESS in the replum. (See poster
by Roeder et al.) While much work has been done defining the regulatory
network that controls the definition of the valve margin, very little is known
about the mechanisms which establish this network. We will present work
that uncovers new layers of regulation controlling the development of the fruit
which unites genetic pathways that control lateral organ shape and polarity
with those that control valve margin identity.
T01 Development 1 (Flower, Fertilization, Fruit, Seed)