15th International Conference on Arabidopsis Research - TAIR

T02-011
A model of Arabidopsis leaf development
Sarah Cookson(1), Christine Granier(1)
1-Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux (LEPSE), ENSAM-INRA,
2 Place Viala, 34060 Montpellier, France
There are internal genetic differences in leaf development between species,
superimposed upon this, regulation of leaf growth responds to environmental
signals. The aim of this work was to investigate the regulation of leaf growth
in Arabidopsis thaliana by genetic (mutation) and environmental (light) factors.
Two leaf development mutants were selected from EMS-induced mutants
(Berná et al., 1999). One with increased (ron2-1) and one with reduced
(ang4) leaf area. Wild type (Landsberg erecta, Ler) and mutant plants were
grown in rigorously controlled environmental conditions and subjected to
various light treatments.
In all light conditions, ron2-1 produced leaves with significantly higher areas
than the wild type while ang4 produced leaves with significantly lower areas.
In all genotypes, final leaf area was reduced by reduced incident light. Finally,
the internal and external regulatory factors exploited in this study produced a
16-fold difference between the largest and smallest mean final leaf 6 area.
They also caused differences in all leaf growth variables such as duration
of leaf expansion, relative and absolute leaf expansion rates, leaf initiation
rate, leaf emergence rate and, at the cellular scale, epidermal cell size and
epidermal cell number. The presence of any relationships between the leaf
growth variables was investigated in this large range of growth curves and a
model of leaf development was created from these relationships.
Our results indicate that conditions affecting early events of leaf development
(initial relative expansion rate, cell division) have an impact on late processes
such as the duration of expansion or final cell size. Such a model could help
to resolve the existing controversy about the role of cell division in organ
formation (Fleming, 2002) and also to identify a role for endoreduplication in
leaf development.
Berná et al., 1999, Genetics, 152:729-742
Fleming, 2002, Planta, 216 :17-22
T02 Development 2 (Shoot, Root)
T02-012
Synergistic interaction of ERECTA-family receptorlike
kinases regulate cell proliferation, patterning,
and organ growth
Keiko U. Torii(1), Chris T. Berthiaume(1), Emi J. Hill(1), Lynn J. Pillitteri(1), Elena D.
Shpak(1)
1-Department of Biology, University of Washington, Seattle, WA 98195 USA
Growth of plant organs relies on coordinated cell proliferation followed by cell
growth, but nature of cell-cell signal that specifies organ size remains elusive.
The Arabidopsis receptor-like kinase (RLK) ERECTA regulates inflorescence
architecture. Our previous study using a dominant-negative fragment of
ERECTA revealed the presence of redundancy in the ERECTA-mediated signal
transduction pathway. We found that Arabidopsis ERL1 and ERL2, two functional
paralogs of ERECTA, play redundant but unique roles in a subset of the
ERECTA signaling pathway and that synergistic interaction of three ERECTAfamily
RLKs define aerial organ size. While erl1 and erl2 mutations conferred
no detectable phenotype, they enhanced erecta defects in a unique manner.
Overlapping but distinct roles of ERL1 and ERL2 can be largely ascribed to
their intricate expression patterns rather than their functions as receptor
kinases. Loss of the entire ERECTA family genes led to striking dwarfism,
reduced organ size, and abnormal flower development, including defects in
petal polar expansion, carpel elongation, and anther and ovule differentiation.
These defects are due to severely reduced cell proliferation. We propose that
ERECTA-family RLKs act as redundant receptors that link cell proliferation
to organ growth and patterning. The specific roles of ERECTA-family RLKs
during epidermal cell-type specification and patterning will be discussed.
Shpak et al. (2003) Plant Cell 15: 1095-
Shpak et al. (2004) Development 131: 1491-
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin