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

393 The Protein-protein Interactions of the RCD1 Protein And Their Role in Plant Stress
Signaling
Pinja Jaspers, Tiina Kuusela, Jaakko Kangasjarvi
Dept. of Biol. & Env. Sci, University of Helsinki
RCD1 (radical-induced cell death1) is an Arabidopsis thaliana protein whose function is essential in regulating
reactive oxygen species-related signaling. The gene was originally identified through an ozone sensitive mutant rcd1
that is not only sensitive to increased levels of ozone and superoxide but also has several alterations in its hormonal
signaling. The Arabidopsis genome contains a close homolog of RCD1 called SRO1 and the characterization of these
two proteins will be conducted in parallel.
There is no known biochemical function for RCD1 protein but it is thought to be localized to the nucleus and to have
two domains involved in protein-protein interactions (WWE domain and a ”C-terminal domain”). In addition, RCD1
contains the catalytic core of ADP-ribosyl transferases and the protein sequence contains many potential post-translational
modification sites. Available DNA microarray data suggests that the regulation on the RNA level is not strong and this,
combined with the predictions of the protein structure, indicates post-translational regulation of the protein.
We have constructed a yeast 2-hybrid library and used it to search for interacting proteins to RCD1 and SRO1. Several
interesting proteins were discovered (e.g. the transcription factor DREB2A) and the confirmation of these interactions
in planta is ongoing. To elucidate the post-translational regulation of RCD1 we have studied its protein levels in wild
type plants and in the rcd1 mutant and sro1 knock-out plants.
The information gained by the biochemical characterization of RCD1 will be combined with systemic biology
approaches to gain insights to the regulation and transmission of plant stress signaling.
394 The role of a bZIP transcription factor in sugar signaling in Arabidopsis thaliana
Shin Gene Kang 1 , John Price 1 , Pei-Chi Lin 2 , Jyan-Chyun Jang 1, 2
1
Plant Biotech Center and Department of Horticulture and Crop Science, Ohio State University, Columbus,
OH 43210, 2 Plant Biotech Center and Department of Plant Cellular and Molecular Biology, Ohio State
University, Columbus, OH 43210
Regulation of cell signaling can occur at many different levels. One such signaling mechanism is the interaction
between DNA elements and DNA-binding transcription factors (TFs), which can act as a regulatory circuit to turn on
or turn off gene expression. Despite the fact that at least 10% of all Arabidopsis genes are sugar responsive, very few
regulatory circuits are known to be associated with sugar signaling. We hypothesize that sugar-responsive TFs play key
roles in sugar signaling and TFs are likely control switches in an interconnected regulatory network. We have chosen a
sugar-responsive bZIP transcription factor as a model to test this hypothesis. Gene expression analyses indicate that the
bZIP is highly sensitive to sugar and sugar-repression of the bZIP requires hexokinase activity. Reverse genetic analyses
indicate that the bZIP is involved in sugar-dependent growth responses. Because the bZIP knockout plants grow more
vigorously than that of the WT on the sugar-free MS medium, we hypothesize that the bZIP may be involved in nutrient
utilization. In addition, bZIP knockout plants are tolerant to the high salt that otherwise causes stunted root growth in
the WT. Together these results suggest that the bZIP may work at a point where crosstalk between nutrient and stress
signals takes place. To identify the upstream regulators of the bZIP, we have found several putative sugar responsive cisregulatory
elements in the promoters of bZIP and its co-expressed genes. To further understand the regulatory network,
we will use ChIP-on-chip technique to identify downstream targets of the bZIP.