15th International Conference on Arabidopsis Research - TAIR

T09-017
Interaction between pRb and FIE polycomb protein,
point at a possible mechanism regulating endosperm
development
Assaf Mosquna(1), Aviva Katz(1), Susana Shochat(2), Gideon Grafi(3), Nir Ohad(1)
1-Department of Plant Sciences, Tel-Aviv University, Tel Aviv, 69978, Israel
2-The Hebrew University of Jerusalem, Jerusalem, 21249,Israel
3-The Weizmann Institute of Sciences, Rehovot, 76100, Israel
Inactivation of the Arabidopsis FERTILIZATION INDEPENDEDENT ENDOSPERM
(FIE) protein induces division of the central cell of the embryo sac, leading to
endosperm development in absence of fertilization. The mechanism whereby
FIE regulates this process is largely unknown. Since FIE protein encode for
an LxCxE motif at the its C-terminal, we postulated that activation of central
cell division in fie plants may result from improper interaction with the cell
cycle regulatory element, the retinoblastoma protein (pRb) which can bind to
different proteins, among other, via the LxCxE motif. Pull-down and surface
plasmon resonance (Biacore) assays demonstrated that FIE interacts in-vitro
with the Arabidopsis (AtRb), maize (ZmRb) and human Rb (HuRb). The
interaction of FIE with ZmRB and HuRb in the yeast two-hybrid system, are
in agreement with previous results describing interactions between pRb and
different members of the polycomb protein family in mammals and plants.
Moreover these results support the possibility that FIE-pRb interaction may
occur also in planta. Mutational analysis, show that FIE-RB interaction does
not occur via the LxCxE motif of the FIE protein nor via the pocket B domain
of pRb. These results suggest that FIE may restrain embryo sac central cell
division, at least partly, through interaction with pRb, and suppression of
pRb-regulated genes.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T09-018
A ROS Repressor-Mediated Binary Regulation
System for Control of Gene Expression in Transgenic
Plants
Ulrike Schäfer(1), Dwayne Hegedus(1), Nicholas Bate(1), Abdelali Hannoufa(1)
1-Molecular Genetics Section, Agriculture and Agri-Food Canada, Saskatoon Research Centre,
107 Science Place, Saskatoon, SK, Canada S7N 0X2
We describe a novel binary system to control transgene expression in plants.
The system is based on the prokaryotic repressor, ROS, from Agrobacterium
tumefaciens, optimized for plant codon usage and for nuclear targeting
(synROS). The ROS protein bound in vitro to double stranded DNA comprising
the ROS operator sequence, as well as to single stranded ROS operator DNA
sequences, in an orientation-independent manner. A synROS-GUS fusion
protein was localized to the nucleus, whereas wtROS-GUS fusion remained
in the cytoplasm. The ability of synROS to repress transgene expression
was validated in transgenic Arabidopsis thailana and Brassica napus. When
expressed constitutively under the actin2 promoter, synROS repressed the
expression of the reporter gene GUS linked to a modified CaMV35S promoter
containing ROS operator sequences in the vicinity of the TATA box and
downstream of the transcription initiation signal. Repression ranged from
32% to 87% in A. thaliana, and from 23% to 76% in B. napus. These results
are discussed in relation to the potential application of synROS in controlling
the expression of transgenes and endogenous genes in plants and other
organisms.
Schäfer et al., (2004) Transgenic Res. 13: 109-118
T09 Genetic Mechanisms (Transcriptional and Chromatin Regulation)