15th International Conference on Arabidopsis Research - TAIR

T05-061
Elongation factor Tu ¯ a novel PAMP involved in plant
defence
Gernot Kunze(1), Pascal Bittel(1), Anne Caniard(1), Delphine Chinchilla(1), Silke
Robatzek(1), Cyril Zipfel(1), Thomas Boller(1), Jürg Felix(1)
1-Botanical Institute, Section of Plant Physiology, Hebelstrasse 1, CH-4056 Basel, Switzerland
As all multi-cellular organisms plants have evolved sensitive perception
systems to detect microbial invasion. Similar to the innate immune system in
animals and insects, some of these detection systems are targeted against
epitopes characteristic for fungi or bacteria in general ¯ so called PAMPs (Pathogen-Associated
Molecular Patterns). In earlier work, we identified flagellin,
the major building block of the bacterial flagellum, as a PAMP recognized by
many plant species. In this study, by using a bacteria strain lacking a flagellin
gene, we demonstrate that the most abundant and conserved bacterial protein,
elongation factor Tu (EF-Tu), functions as a PAMP in Arabidopsis thaliana.
By using a combined approach of chromatography, enzymatic digestions and
MALDI-MS we could restrict elicitor-activity to an epitope of 18 amino acids.
Elf18, a peptide representing this domain, is able to induce oxidative burst,
increased ethylene biosynthesis, massive seedling growth inhibition, and
expression changes in a high number of genes at subnanomolar concentrations
as potent as flagellin (flg22). Moreover, elf18 signalling acts through
a MAP kinase cascade, and pre-treatment of Arabidopsis leaves with elf18
induces increased resistance to subsequent infection with pathogenic Pseudomonas
syringae pv. tomato. Clearly, Arabidopsis contains a high affinity
binding-site for elf18 that cannot be competed by flg22. This demonstrates
that elf18 perception involves a different receptor than FLS2. Currently we
are identifying potential receptor candidates by reverse and forward genetic
screens. Our experiments indicate that Arabidopsis thaliana has a highly
specific recognition system for bacterial EF-Tu, which elicits a broad array of
defence responses.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T05-062
Functional Genomics of Arabidopsis Heat Stress
Transcription Factors (Hsfs)
Sachin Kotak(1), Markus Port(1), Arnab Ganguli(1), Frank Bicker(1), Pascal von
Koskull-Döring(1)
1-1Department of Molecular Cell Biology, Biocenter N200, 3OG, Goethe-University Frankfurt,
Marie-Curie-Str. 9, D-60439 Frankfurt, Germany
Heat stress transcription factors (Hsfs) are the major regulators of the plant
heat stress response. Sequencing of the Arabidopsis genome revealed the
existence of 21 ORFs encoding putative Hsfs assigned to classes A, B and C.
Here we present results of a functional genomics approach to the Arabidopsis
Hsf family focused on the analysis of their C-terminal domains harboring
conserved modules for their function as transcription factors and their
intracellular localization. Using reporter assays in tobacco protoplasts and
yeast as well as GST pull-down assays, we demonstrate that short peptide
motifs enriched in aromatic and large hydrophobic amino acid residues
embedded in an acidic surrounding (AHA motifs) are essential for transcriptional
activity of class A Hsfs. In contrast to this, class B and class C Hsfs
lack AHA motifs and have no activator function on their own. We provide also
evidence for the function of a leucine-rich region at the very C-terminus as a
nuclear export signal (NES) of class A Hsfs. Sequence comparison indicates
that the combination of a C-terminal AHA motif with the consensus sequence
FWxxF/L,F/I/L as well as the adjacent NES represent a signature domain for
plant class A Hsfs, which allowed to identify more than 60 new Hsfs from the
EST data base.
Kotak et al. (2004) Plant J. 38, in press
Nover et al. (2001) Cell Stress Chap 6: 177-189
T05 Interaction with the Environment 2 (Biotic)