75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

141 HAESA and HAESA-like 2 Activate Floral Organ Abscission In An Ethylene-Independent
Manner
Sung Ki Cho, David Chevalier, Kevin Lease, Jason Doke, John Walker
University of Missouri
Organ abscission involves the regulated separation of cell layers to cause detachment of an organ from a plant. Our
goal is to understand the molecular basis of this process. HAE and HSL2 exhibit similar promoter::GUS expression at
floral abscission zones. Single knockout mutant lines of either gene do not show any phenotype, but the hae hsl2 double
knockout mutant show an abscission-defect phenotype. The abscission defect observed in the double mutant could
either be due to the inability to differentiate the abscission zone, or an inability to activate the cell separation process.
Longitudinal sections through the abscission zone were examined by light microscopy and the fracture planes at the
abscission zone when petals were forcibly removed were examined by scanning electron microscopy. These observations
showed that the abscission zone in the hae hsl2 double mutant appears structurally normal. Furthermore, the hae hsl2
petal breakstrength at all flower positions was similar to that of wild type flowers that have not yet begun to abscise their
petals. Taken together, these data support the idea that the role of HAE and HSL2 is to activate cell separation, rather
than promote the differentiation of the abscission zone. Ethylene is also known to promote abscission; therefore we
tested the ethylene-induced triple response and the effect of exogenous treatment on floral organ in the double mutant,
revealing that HAE and HSL2 act independently of ethylene. We hypothesize that HAE and HSL2 activate abscission
in an ethylene-independent manner by inducing the expression of enzymes that promote cell separation.
142 The Arabidopsis EARLY IN SHORT DAYS 7 (ESD7) Locus Encodes The Catalytic Subunit of
DNA POLYMERASEε
Ivan Del Olmo 1 , Mar Martin-Trillo 2 , Jose Martinez-Zapater 2 , Manuel Pineiro 1 , Jose Jarillo 1
1
Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria (INIA), Departamento de
Biotecnologia, 28040 Madrid, Spain., 2 Centro Nacional de Biotecnologia; Departamento de Genetica Molecular
de Plantas, Cantoblanco, Madrid 28049, Spain.
The suitable control of the floral transition is crucial for reproductive success in flowering plants. In the last years,
several early-flowering mutants have been characterized although much of their interactions with the inductive pathways
of flowering are not known. In a collection of Ds-containing T-DNA lines in Ler background, we have isolated the esd7
mutation, which causes early flowering independently of photoperiod conditions. Because the Ds element did not cosegregate
with the early flowering phenotype, the ESD7 locus has been identified by a map-based cloning approach. ESD7 encodes
the catalytic subunit of DNA polymerase ε (AtPOL2A), which is essential for the correct development and viability of the
embryo (Ronceret et al., 2005, The Plant Journal 44:223-236). The esd7-1 mutation is affecting a conserved glycine residue
boundering the C1 region of the protein. RT-PCR expression analysis for ESD7/AtPOL2A shows a very low expression
level in most of the analyzed tissues; however, this expression is markedly increased by exposure to genotoxic agents; a 1
Kb promoter fusion AtPOL2A:GUS reveals that this gene is mainly expressed in the shoot and the root apical meristems
and the vascular tissues at the seedling stage. The mutant phenotype is quite pleiotropic resulting in plants smaller in size
and less vigorous than wild-type plants; microscopic analyses show that the epidermal cell size of mutant leaves is increased
in comparison to wild type, although the cell number is smaller. Besides, the esd7-1 mutant shows narrowed leaves and
alterations in the pattern of vegetative growth, mainly a reduction of the adult vegetative phase; in addition, the development
of the root is also affected in the esd7-1 mutant, as it has been described for another hypomorphic allele of this gene (Jenik
et al., 2005, The Plant Cell 8:3362-3377); the primary root of the mutant displays a significant decrease in elongation that
is accompanied by a higher production of adventitious roots. Genetic analysis between esd7-1 and mutants affected in
flowering inductive pathways suggests that flowering inhibition mediated by ESD7 may occur through different pathways
and that is totally dependent on FT and SOC1 expression. Expression analysis of the floral integrators FT and SOC1 and
the flowering time genes such as FLC and CO in esd7-1 mutant will be presented.