75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

289 Resistance to Xanthomonas campestris pv. campestris in Arabidopsis thaliana
Laure Perchepied, Raimana Louette, Damien Meyer, Kroj Thomas, Dominique Roby
LIPM CNRS/INRA Toulouse
Xanthomonas campestris pv. campestris (Xcc) is a model pathogen which causes black rot disease on crucifers. For
studying the interaction of Xcc with the model plant Arabidopsis thaliana, a wound inoculation test was developed in
the laboratory (Meyer et al., 2005). The genetic determinism for resistance to Xcc in Arabidopsis thaliana is not yet
understood. To get an insight into this process, we first tested Arabidopsis mutants impaired in resistance to different
pathogens in order to determine if known signalling components of resistance are involved in resistance to Xcc. While
mutants impaired in specific resistance to other pathogens do not seem to be affected in resistance to Xcc, different pad
and eds mutants which possess reduced basal resistance, such as pad1, were found to be susceptible to Xcc.
Then, we started to investigate the genetic bases of resistance to Xcc in Arabidopsis without a priori. We analysed
various Arabidopsis accessions and identified high natural variation for resistance to Xcc. The accession Columbia 5
(Col-5) is for example resistant to Xcc whereas Kashmir (Kas) is susceptible. In order to identify the loci that confer
resistance, we analysed a recombinant inbred ( RILs) population (110 lines) derived from a cross between Col-5 and
Kas. We performed four independent tests in a complete randomized design. The RILs distributions showed a continuous
variation of resistance between the resistant accession Col-5 and the susceptible accession Kas, suggesting a polygenic
control of resistance. Quantitative trait loci (QTL) analyses were performed on the four independent tests and allowed
the detection of one major and 3 minor QTLs. In order to characterize the locus corresponding to the major QTL, we
used heterogeneous inbred families (HIF) from the RIL population. These HIFs allowed us to validate the effect of the
major QTL. Fine mapping of this locus is now underway. With the development of numerous markers, we could reduce
the confidence interval of the QTL to 2.3Mb.
Meyer et al., Mol Plant Pathol (2005) 6 (3), 327-333.
290 Functional characterization of the ACD11 protein
Nikolaj H. Petersen 1 , Peter Brodersen 2 , Margerita Malakova 3 , Daniel Hofius 1 , Lea Mckinney 1 , Helen Pike 3 , Rhoderick
Brown 3 , John Mundy 1
1
Institute of Molecular Biology, University of Copenhagen, Denmark, 2 Institut de Biologie Moleculaire des
Plantes CNRS, Strasbourg, France, 3 Hormel Institute, University of Minnesota, Austin, Minnesota, USA
Knockout of the Arabidopsis Accelerated Cell Death 11 gene leads to a defense-related, constitutive programmed cell
death (PCD) reaction and the recessive acd11 mutant is non-viable. The ACD11 protein shows homology to mammalian
glycolipid transfer protein (GLTP), that transfer glycosphingolipids between membranes. However, ACD11 was shown
to transfer the sphingobase sphingosine, a different substrate than GLTP. Sphingolipids are important components of
plasma membranes, but spingobases such as ceramide and sphingosine have also been shown to have signaling properties.
Mutational analysis of GLTP revealed amino acids that are required for transfer activity, and that are conserved in
ACD11. We are currently testing whether corresponding site-directed mutant ACD11 forms can complement the acd11
phenotype. Preliminary data suggest that at least two of these mutants complement, but that they are affected in aspects of
plant defence. We are also using a previously described FRET based lipid transfer assay to further elucidate the substrate
specificity of ACD11, as well as testing the activity of mutant forms of ACD11.