15th International Conference on Arabidopsis Research - TAIR

T09-039
Plant specific GAGA-binding proteins regulate
MADS-box gene expression through DNA
remodelling
Maarten Kooiker(3), Chiara A. Airoldi(1), Prescilla S. Manzotti(2), Bilitis Colombo(3),
Laura Finzi(2), Martin M. Kater(3), Lucia Colombo(1)
1-Dipartimento di Biologia, Sezione di Botanica Generali, Universita di Milano, Italy
2-Dipartimento di Biologia, Sezione di Fisiologia Vegetale e Fotosintesi, Universita di Milano, Italy
3-Dipartimento di Scienze Biomoleculari e Biotechnologie, Universita di Milano, Italy
In Drosophila the Trithorax-like locus encodes several GAGA-binding proteins
(GBPs) that bind to GAGA-DNA repeats and regulate the expression of several
genes, including themselves and the homeotic genes Ultrabithorax and
Engrailed (reviewed in 1). The GBPs have been reported to co-localize with
polycomb response elements and trithorax response elements and have been
reported to be important in both gene repression and activation pathways.
This regulation is mediated by the interaction of GBP with several protein
complexes like NURF, SIN3 and SAP18 or directly with PC or TRX.
In Soy bean, Barley and Arabidopsis proteins that bind to GA-rich DNA-elements
have been reported recently (2,3,4). Though they seem to be unrelated
to the Drosophila GBPs, they share a surprising number of functions.
We show that the Arabidopsis GBP Basic Penta Cystein 1 (BPC1) binds to
a DNA motif RGARAGRRA, which is several times present in the regulatory
sequence of the homeotic MADS-box gene STK as well as in the regulatory
sequence of BPC1 and BPC2. The expression of these genes is altered in the
bpc1 and bpc2 mutants, showing that in Arabidopsis the homeotic gene STK
and BPC1/2 are regulated by BPC1/2. With TPM-experiments we show that
BPC1 is able to form stable DNA-loops by binding to several GAGA-elements
present in the STK regulatory sequence. Like in Drosophila multiple binding
sites are required for the formation and stabilization of these loops. This loop
is possibly mediated by the formation of dimers or oligomers, since we show
that the BPC1 and BPC2 proteins are able to form homo or heterodimers, like
the Drosophila GBPs.
1 Trends in Genet. 20, 15-22
2 Plant Physiol. 129, 1788-1794
3 Plant J. 37, 426-438
4 Plant J. 34, 813-826
T09 Genetic Mechanisms (Transcriptional and Chromatin Regulation)
T09-040
The influence of the light period on redox regulation
and stress responses
Beril Becker(1), Simone Holtgrefe(1), Sabrina Jung(1), Regina Brockmann(1),
Andrea Kandlbinder(2), Karl-Josef Dietz(2), Jan E. Backhausen(1), Renate
Scheibe(1)
1-Pflanzenphysiologie, Fachbereich Biologie/Chemie, Universität Osnabrück,
2-Fakultät für Biologie, Lehrstuhl für Biochemie und Physiologie der Pflanzen, Universität Bielefeld
Under natural conditions, plants are subjected to an environment in which
several parameters such as light or temperature can change dramatically for
periods which can last for seconds or even for days. Plants possess a large
set of mechanisms, such as the malate valve, to prevent damages in the
short-term. However, when environmental alterations persist, a response on
the genetic level is induced, possibly mediated by altered redox states in the
chloroplast. The type of acclimation strictly depends on the developmental
stage of the plants and and on the duration of the light period. To investigate
the different responses, Arabidopsis plants were grown in low light (150 µE)
either in short days (7.5 h light ) or long days (16 h light period), and then
transferrred into high light (350-800 µE) at 12°C. The plants grown in short
days responded with a quick increase in NADP-malate dehydrogenase activation
state, but persisting overreduction revealed a new level of regulation of
the malate valve. Activity measurements and Northern-blot analyses indicate
that upregulation of the NADP- malate dehydrogenase transcript amount
starts a few hours after the onset of the stress. Using macroarrays, additional
changes in gene expression were identified. The transcripts of several enzymes
of glutathione metabolism and of some photosynthetic genes increased.
The cellular glutathione content increased, but its redox state remained
unchanged. A completely different situation was obtained in plants grown in
long-day conditions. Here, neither NADP-malate dehydrogenase nor other
photosynthetic enzymes changed, but the expression of several antioxidative
enzymes increased strongly. We conclude that the endogenous systems
that measure the daylength interact with redox regulation, and override the
interpretation of the signals, i. e. they redirect redox-mediated acclimation
signals from a more efficient light usage and from redox poising in short days
towards the prevention of oxidative damages in long days.
This work is financially supported by a grant from the Deutsche Forschungsgemeinschaft (FOR
387, TP1 and TP3).
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin