15th International Conference on Arabidopsis Research - TAIR

T05-023
An Arabidopsis mutant with decreased non-host
penetration resistance has increased resistance to a
host pathogen.
Monica Stein(1), Bi-Huei Hou(1), Shauna C Somerville(1)
1-Carnegie Institution of Washington, Plant Biology
Plants are constantly exposed to a wide variety of pathogens. However, a
given plant species is host to only a subset of these pathogens. Resistance
to pathogens outside this subset is termed non-host resistance. Non-host
resistance is thought to be multigenic, non-specific, and durable. In contrast,
the resistance of certain genotypes of an otherwise susceptible species to
a pathogen is termed host resistance. This type of resistance often follows
gene for gene interactions and is typically short lived in the field. Isolating
plant factors that affect non-host resistance may lead to a better understanding
of non-host resistance.
Arabidopsis is a host to the powdery mildew Erisyphe cichoracearum, and
a non-host to Blumeria graminis f.sp. hordei, a pathogen of barley. 12,000
EMS-mutagenized plants were screened for increased penetration of the
non-host mildew on Arabidopsis. Four different loci were identified. Two of
these were allelic to pen1 and pen2, penetration mutants isolated simultaneously
in other labs (1)(Hans Thordal-Christensen and Paul Shulze-Lefert,
personal communication). A third locus, pen3, is unique in that it permits
both increased penetration and increased hyphal growth by the non-host
fungus. In contrast to pen2 and the fourth locus pen4, which are hyper-susceptible
to the host powdery mildew, pen3 is resistant to the host fungus and
this resistance is salycilic acid-dependent. The pen3 phenotype is caused
by mutations in an ABC transporter. Microarray analysis, metabolite profiling,
and localization experiments are underway.
1. Thordal-Christensen et al., Nature (2003)
T05 Interaction with the Environment 2 (Biotic)
T05-024
Putative plant molecular target molecules of the
pathogenicity protein effector POPP1 secreted by
Ralstonia solanacearum.
Laurent Sauviac(1), Nigel H. Grimsley(2)
1-Laboratoire des Interactions Plantes-Microorganismes, P.O. Box 27, Auzeville , F-31326 Castanet
Tolosan cedex, France
2-Friedrich Miescher Institute, Maulbeerstrasse 66, CH 4058, Basel, Switzerland.
Analysis of the genomic sequence of the plant pathogen R. solanacearum
permitted the identification of numerous open reading frames that may
encode molecules effecting pathogenicity. PopP1 is such a protein showing
homology to YopP of Yersinia, which is injected into animal cells by the
conserved type III secretion system. A R. solanacearum strain carrying a
mutation in PopP1 was unexpectedly more aggressive on susceptible tomato
and Arabidopsis lines, but became virulent on normally resistant genotypes
of Petunia, the latter observation thus showing that PopP1 can behave as an
avirulence gene. We show that, in contrast to YopP, PopP1 does not interact
with map kinase kinases in the yeast two-hybrid system. We have identified
three possible target molecules of PopP1 by screening a cDNA library of the
model host plant Arabidopsis thaliana using the yeast two-hybrid system.
One of these proteins (AtSNX1) may be involved in protein sorting, since in
mammalian systems its homologues are implicated in the internalisation of
an important class of membrane receptor molecules. Preliminary results obtained
using transient expression of GFP-fused hybrid proteins in transfected
protoplasts suggest that both PopP1 and AtSNX1 are cytoplasmically located.
Currently, we are attempting to verify the interactions observed in yeast by
co-immunoprecipitation in vitro.
Salanoubat, M., et al. (2002). Nature 415, 497-502.
Lavie et al. 2002. Mol. Plant-Microbe Interact 15 :1058-1068.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin