15th International Conference on Arabidopsis Research - TAIR

T05-029
An Arabidopsis Mlo knock-out mutant phenocopies
the barley mlo broad spectrum powdery mildew
resistance phenotype
Chiara Consonni(1), H. Andreas Hartmann(1), Paul Schulze-Lefert(1), Ralph
Panstruga(1)
1-Max-Planck Institute for Plant Breeding Research, D-50829 Köln, Germany
Powdery mildew is a common disease of plants. A range of powdery mildew
species colonize almost all plant species. In temperate climate, powdery
mildew infections cause severe yield losses in a wide range of crops.
Recessively inherited loss-of-function alleles (mlo) of the barley Mlo gene
confer resistance that is effective against all known isolates of the barley
powdery mildew fungus, Blumeria graminis f. sp. hordei. In susceptible Mlo
wild type plants, the fungus potentially manipulates the protein encoded by
this gene for plant cell invasion. Until recently, it was unclear whether mlo
resistance represents a species-specific phenomenon restricted to barley.
Although Mlo homologs are found in all flowering plants examined to date it
was uncertain whether powdery mildews target MLO proteins in other plant
species for plant cell invasion. Our results demonstrate that mlo resistance
can be induced in the model plant Arabidopsis by inactivation of a particular
of the 15 Mlo homologs. The respective Arabidopsis insertion mutants were
found to be highly resistant against the virulent powdery mildew fungus,
Golovinomyces orontii, while infection phenotypes to the bacterial pathogen
Pseudomonas syringae, and the oomycete Peronospora parasitica appeared
unaltered. Similar to barley mlo resistant plants, the powdery mildew
sporelings fail to switch from surface to invasive growth in the Arabidopsis
mutants. No recognizable pleiotropic effects are detectable in the mutants.
These data demonstrate that mlo resistance is effective in both major clades
of flowering plants, suggesting that the role of MLO proteins for colonization
by powdery mildews is ancient and evolutionarily conserved.
Panstruga, R. & Schulze-Lefert, P.; Microbes and Infection 5, 429-437 (2003).
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T05-030
Genetic variation of powdery mildew resistance
in Arabidopsis thaliana as a resource for the
identification of novel host “compatibility factors”
Katharina Goellner(1), Ralph Panstruga(1)
1-Max-Planck-Institute for Plant Breeding Research, Carl-von-Linné-Weg 10, 50939 Koeln,
Germany.
In a compatible microbe-plant-interaction, host “compatibility factors” are required
for the establishment and maintenance of the infection. Consequently,
loss of function of such host genes is predicted to result in incompatibility
and therefore resistance against the pathogen. This recessively inherited
resistance functions without constitutive activation of defense responses and
can be effective for single or closely related pathogen species. There are
already several single recessive loci known in a range of plant species that
confer resistance to several types of pathogens.
However, genetic analysis in a single genotype is likely to unravel only a
subset of potential host compatibility factors because of genetic redundancy
or functional specialization. We therefore intend to exploit natural genetic
variation within Arabidopsis thaliana as an additional resource for the identification
of novel genes conferring powdery mildew resistance, preferably due
to absence of specific host compatibility factors.
We determined resistance phenotypes of selected accessions with the
powdery mildew fungus Golovinomyces orontii, crossed the resistant accessions
with the susceptible accession Col-0 and selected candidate genes
after analysis of the respective F1 and F2 generation for putative single and
recessive loci.
In first two candidate accessions conferring resistance, Shadara and Sorbo
(Tadjikistan), the “compatibility” locus was mapped to the lower arm of
chromosome III by SSLP markers in Sorbo and with a Bay-0 x Shadara RIL
population in Shadara. It remains to be determined how resistance is achieved
and if it is due to the same locus in these accessions.
T05 Interaction with the Environment 2 (Biotic)