15th International Conference on Arabidopsis Research - TAIR

T05-045
Investigating the basis for differential functions
between Arabidopsis SGT1a and SGT1b
Shigeyuki Betsuyaku(1), Laurent D. Noël(1, 2), Paul R. Muskett(1), Jane E. Parker(1)
1-Department of Plant-Microbe interactions, Max-Planck-Institute for Plant Breeding Research,
Carl-von-Linné-Weg 10, D-50829 Köln, Germany
2-Laboratoire de Biologie du Développement des plantes, UMR CNRS-CEA-Université méditerrannée
6191, DEVM, CEN Cadarache, F-13108 Saint Paul lez Durance Cedex, France
SGT1, which has molecular features of a co-chaperone, is a positive regulator
of R (Resistance) protein-mediated defence in diverse plant species.
Recent studies indicate that SGT1 together with RAR1 and HSP90 may
be required for R protein accumulation. SGT1 is an essential gene, and in
Arabidopsis there are two recently duplicated highly sequence-related copies,
AtSGT1a and AtSGT1b. AtSGT1b, but not AtSGT1a, is genetically required
for resistance mediated by a subset of R genes and phytohormone signaling
controlled by at least two plant SCF E3 ligases (SCFTIR1 and SCFCOI1).
However, a double sgt1a/sgt1b is embryo lethal, indicating that AtSGT1a
and AtSGT1b have overlapping essential functions early in development.
To understand further the molecular basis for differential activities between
AtSGT1a and AtSGT1b, we are analyzing their mode of expression at the
protein level and their transcriptional activities using AtSGT1a or AtSGT1b
promoter GUS fusions in a wild type background. AtSGT1a/AtSGT1b-promoter-swap
and AtSGT1a over expressing constructs were also made to
assess their potential to complement sgt1b-3 phenotype in R gene-mediated
resistance and phytohormone signaling. Our analysis will determine if the
different functions of AtSGT1a and AtSGT1b lie at the level of their mode of
expression or the respective protein activities. Current progress in this study
will be presented.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T05-046
Cloning of Arabidopsis homologues of IAA-
amidohydrolases from Chinese cabbage and
expression during the development of clubroot
disease
Astrid Schuller(1), Jutta Ludwig-Müller(1)
1-TU-Dresden, Institute of Botany, 01062 Dresden
Clubroot disease is caused by an obligate biotroph organism called Plasmodiophora
brassicae, who infects roots of all members of the Brassicaceae.
In infested soil the resting spores of the pathogen can survive for over ten
years and the infection includes a primary cycle in the root hairs followed by
the secondary cycle during which the secondary zoospores enter the root
itself. Each zoospore develops into a plasmodium which spreads through
the host cells. The pathogen development proceeds from young plasmodia
over vegetative plasmodia to a mass of resting spores. Correlated with the
development of vegetative plasmodia an abnormal growth of the root is
observed, induced by enhanced cell enlargement and cell proliferation. One
interesting point in the life cycle of Plasmodiophora is the hormonal control
of these processes in the host cells. It has been reported that they correlate
with an increase in cytokinins and auxins, especially IAA. One source of free
IAA is the release from conjugates with amino acids. The catalyzing enzymes
for these reactions are the IAA-amidohydrolases. Genes for these enzymes
have first been characterized in Arabidopsis thaliana but since clubroot disease
is economically important in crops and the time course of infection as
well as the localization of the plasmodia seems to vary between Arabidopsis
thaliana and Brassica rapa we started to isolate IAA-amidohydrolases from
Chinese cabbage. We were able to isolate cDNA fragments with homology
to IAR3, ILL2, ILL6, ILL3 and ILR1 out of infected roots of Brassica rapa at
different time points of infection, as well as of uninfected seedlings and
leaves and stems of uninfected plants. Using a RACE approach we have so
far isolated full length cDNAs from the following amidohydrolases like genes:
IAR3, were we found 2 different clones varying in the 5'-region of the genes,
ILL2, closely related to IAR3, and ILL6 which is placed in a separate group
in the dendrogram of the IAA-amidohydrolases. Expression studies of the
corresponding genes in infected and uninfected roots using Real Time RT-
PCR revealed a differentially and very stage specific regulation. How far the
observed up-regulation can account for an increased auxin level has to be
further investigated. Heterologous expression studies in E. coli to run in-vitro
enzyme activity assays are under way.
T05 Interaction with the Environment 2 (Biotic)