15th International Conference on Arabidopsis Research - TAIR

T02-007
A novel class of Arabidopsis response regulator
genes, the ectopic expression of which results in
phenocopy of the wol cytokinin-receptor deficient
mutant
Takatoshi Kiba(1), Koh Aoki(2), Hitoshi Sakakibara(2), Takeshi Mizuno(1)
1-Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University
2-Plant Science Center, RIKEN (Institute of Physical and Chemical Research)
Arabidopsis thaliana has a number of response regulators (ARRs) implicated
in the histidine (His) to aspartate (Asp) phosphorelay signal transduction.
According to the current consistent model, both the type-A and type-B ARR
family members play crucial roles in the cytokinin signaling circuitry. However,
this higher plant has a few extra ARRs, on which no attention has been paid
so far. Characterization of these extra ARRs might provide us with new insight
into the His-Asp phosphorelay signal transduction in plants. For this reason,
in this study we extensively examined the natures of such a representative
(named ARR22). Transcripts of ARR22 were expressed predominantly in
reproductive organs, and a GFP::ARR22 fusion protein was localized in the
cytoplasmic space in onion epidermal cells. The purified ARR22 protein had
the ability to undergo phoshorylation in vitro, when incubated with phospho-AHP5,
indicating that ARR22 has the fundamental ability to participate
into a His-Asp phosphorelay pathway in its own right. In plants, transgenic
lines overexpressing ARR22 were characterized (referred to as ARR22-ox),
which showed the characteristic dwarf phenotypes with poorly developed
root systems. The results of Northern blot hybridization with selected sets of
hormone-responsive genes suggested that cytkinin responses are selectively
attenuated in ARR22-ox, while other hormone responses (auxin, ABA and
ethylene) occur normally. The results of microarray analyses with cytokinin-treated
wild-type and ARR22-ox plants further supported the view that
cytokinin responses are globally attenuated in ARR22-ox, at least, at the level
of gene regulation. Finally, we demonstrated that the dwarf phenotypes of
ARR22-ox appear to be phenocopies of the wol mutant, which has a sever
lesion in the AHK4/CRE1 cytokinin-receptor of histidine protein kinase. These
results suggested that ARR22 might also be implicated, directly or indirectly,
in the cytokinin-responsive His-Asp phophorelay signal transdution.
T02 Development 2 (Shoot, Root)
T02-008
Localization and activity of the embryo pattern
regulator BODENLOS
Alexandra Schlereth(1), Jasmin Ehrismann(1), Dolf Weijers(1), Gerd Jürgens(1)
1-Center for Molecular Plant Biology (ZMBP), Developmental Genetics, Universität Tübingen, Auf
der Morgenstelle 3, D-72076 Tübingen, Germany
Embryogenesis in plants transforms the fertilized egg cell into a multicellular
organism with many distinct cell types, organized in a defined pattern.
During this pattern formation, establishment of the embryonic root meristem
requires regulated activity of the transcriptional activator MONOPTEROS
(MP/ARF5), and its repressor BODENLOS (BDL/IAA12), both involved in auxindependent
gene activation. Loss of MP function, or stabilization of BDL leads
to the same phenotype early in embryo development. The root meristem
precursor (hypophysis) does not divide properly, and no root is formed. In
situ hybridization revealed that MP and BDL mRNAs are not expressed in the
hypophysis, but in the adjacent proembryo cells, suggesting non-autonomous
action of MP and BDL, that could involve movement of the proteins themselves,
or cell-to-cell communication through a mobile downstream signal. We
performed a series of experiments to probe the accumulation pattern and the
spatio-temporal activity of the BDL protein. As expected, translational fusions
of BDL to GUS showed the protein to be nuclear and unstable, targeted for
proteasome-dependent degradation by auxin. We will present a detailed
analysis of accumulation patterns of BDL:GUS in the early embryo. To
determine spatial requirements for BDL activity, a dominant stabilized mutant
bdl protein was expressed in restricted embryo domains using GAL4/UAS
expression technology. Expression of the stabilized bdl protein within the
endogenous BDL expression domain reconstitutes the bdl mutant phenotype.
We will present the results of controlled expression of bdl in a variety of cell
types within the early embryo.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin