15th International Conference on Arabidopsis Research - TAIR

T04-079
CHARACTERIZATION OF THE PHOSPHATE SIGNAL
TRANSDUCTION PATHWAY IN ARABIDOPSIS
THALIANA
THIBAUD(1), misson(1), nussaume(1)
1-Laboratory of Plant Development Biology, CEA Cadarache DSV DEVM
Phosphate availability is one of the major limiting factors for plant development.
Plants respond to the level of phosphate available by activating
specific mechanisms to improve phosphate uptake and utilization. These
include molecular and phenotypic changes : numerous genes are regulated
by phosphate (transporters, phosphatases, …) and the root architecture is
drastically modified by phosphate starvation (shorter primary root). Nevertheless,
most of the elements of the phosphate signal transduction pathway are
unknown. We develop in the lab different approaches in order to characterize
the response of the plant Arabidopsis thaliana (WS ecotype) to phosphate
deficiency and to identify the elements of the regulation involved in the
phosphate signal transduction pathway.
The plant response to Pi strarvation was characterized at different levels
: phenotypic (root development, anthocyanin accumulation), biochemical
(potential Pi absorption, lipid composition) and molecular (gene transcripts).
Microarray experiments (Affymetrix microarray) were performed with the
whole genome of Arabidopsis thaliana and allowed the identification of
elements of the metabolic pathways modified in Pi-starved plants and of the
transcriptional regulation of the genes.
Moreover, we used a T-DNA insertion line of Arabidopsis thaliana, a mutant
for the high affinity phosphate transporter AtPT2. The insertion prevents the
transcription of the gene and contains a GUS reporter gene driven by the native
AtPT2 promoter, which permits localization of the gene expression (time
and spatial localization). Mutagenesis of this line will permit identification of
the regulations involved in the phosphate signal transduction pathway.
T04 Interaction with the Environment 1 (Abiotic)
T04-080
Poly(ADP-ribose) Polymerases (PARPs) in Arabidopsis
Charlene Calvert(1), Sue Butcher(1), Mark Coleman(1)
1-University of East Anglia, Norwich, UK
The ability to maintain genomic integrity is essential to the survival of all
organisms. Single-strand breaks in DNA are produced by various endogenous
and exogenous factors, including water, reactive metabolites, ionising
radiation and UV light. One of the responses to many DNA-damaging
stresses is the synthesis of poly(ADP-ribose). This is catalysed by poly(ADPribose)
polymerases (PARPs), eukaryotic enzymes usually found in the
nucleus. Most of our knowledge of PARPs is derived from experiments with
human PARP-1 (hPARP-1). hPARP-1 has a low basal catalytic activity, but
this is greatly increased (~500-fold) in the presence of single-strand breaks
in DNA. hPARP-1 has three functional domains, an N-terminal DNA binding
domain, a central automodification domain, and a C-terminal ‘PARP homology’
region, which contains the catalytic region. Seven PARP genes have been
characterised from humans. hPARP-1 and hPARP-2 have been shown to be
involved in the base excision repair (BER) DNA repair pathway and hPARP-
1 has a demonstrated role in the resistance to genotoxic stresses. I have
identified two mutants in AtPARP-1, the Arabidopsis homologue of human
PARP-1. One mutant has a nonsense mutation about two-thirds into the
protein. It is probable that this is a loss of function mutant as the truncated
protein produced would lack the catalytic domain. Recent results show that
this mutant is more sensitive than wild-type to ionising radiation. These data
thus indicate that AtPARP-1 is required for the repair of damage induced
by this genotoxic stress. The second AtPARP-1 mutant has a missense
mutation located in the PARP homology domain. In contrast to the nonsense
mutant, mutant plants carrying this lesion are more resistant than wild-type
both to ionising radiation and to UV-C. It is thus possible that these missense
mutant plants may have an increased capacity to repair DNA. Interestingly,
both mutant lines exhibit enhanced anthocyanin accumulation. At this time, it
is unclear as to why the two mutations, which have contrasting DNA damage
phenotypes, have the same effect on anthocyanin accumulation, but the
observations clearly indicate a possible link between DNA damage and repair
and anthocyanin biosynthesis.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin