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

299 Identification of genes contributing to nonhost resistance of Arabidopsis thaliana against
Phytophthora infestans
Lore Westphal 1 , Joern Landtag 1 , Mandy Birschwilks 1 , Volker Lipka 2 , Jan Dittgen 3 , Paul Schulze-Lefert 3 , Dierk Scheel 1 ,
Sabine Rosahl 1
1
Leibniz Institute of Plant Biochemistry, D-06120 Halle, Germany, 2 ZMBP, University of Tuebingen, D-72076
Tuebingen, Germany, 3 Max-Planck Institute for Plant Breeding Research, D-50829 Koeln, Germany
Nonhost resistance is a characteristic feature of most interactions between plants and microorganisms, and it
describes the resistance of a complete plant species against all members of a pathogen species. Colonization of a plant
by a nonadapted pathogen is prevented by constitutive and preformed barriers or by the induction of multiple layers of
defense responses upon recognition of the pathogen. One example for an active nonhost resistance is the resistance of
Arabidopsis thaliana against the oomycete Phytophthora infestans, the causal agent of late blight disease on potato and
tomato. In general, P. infestans spores germinate on Arabidopsis leaves and appressorium-like structures are formed.
In most cases, penetration of the epidermal cell wall is averted by papillae formation. However, if the invasion attempt
is successful, additional defense responses are activated, usually resulting in the death of the attacked epidermal cell.
One of our approaches towards the genetic dissection of this phenomenon is a mutant screen based on the penetration
resistance mutant pen2. Pen2 encodes a glycosyl hydrolase, a component of an inducible preinvasion resistance mechanism
that restricts entry of the nonadapted biotrophic ascomycetes Blumeria graminis f. sp. hordei and Erysiphe pisi as well
as the hemibiotrophic oomycete P. infestans (Lipka et al. 2006, Science 310, 1180-1183). In comparison to wild type
Arabidopsis, the pen2 mutant shows an increase in dead epidermal cells after inoculation with P. infestans resulting in
macroscopically visible necrosis. With the aim to impair additional resistance layers, pen2 seeds were EMS-mutagenized,
and approximately 70.000 M2-plants were scored with regard to their hypersensitive response phenotype after inoculation
with P. infestans. So far, 32 mutants with enhanced cell death in comparison to pen2 were isolated, and three mutations
were roughly mapped on chromosome 1, 3 and 5, respectively.
300 Spatial and temporal analysis of host gene expression in response to infection by positivestrand
RNA viruses
Chunling Yang 2 , Rong Guo 2 , Fei Jie 2 , Dan Nettleton 2 , Jiqing Peng 2 , Tyrell Carr 2 , Joanne Yeakley 1 , Jian-Bing Fan 1 ,
Steve Whitham 2
1
Illumina, Incorporated, San Diego, CA, USA, 2 Iowa State University, Ames, IA, USA
Systemic viral infections cause a variety of changes in plant gene expression in Arabidopsis thaliana that may be
spatially and temporally regulated. To investigate this possibility, we used two complementary approaches to profile the
expression of A. thaliana genes as viral infections progressed. First, A. thaliana gene expression was assayed in inoculated
leaves, systemic leaves, and flowers over a 10-day time course using custom high-throughput fiber optic bead arrays.
These arrays represented 388 genes that were primarily selected for these analyses based on a preliminary microarray
experiment. Modulation of gene expression was tightly associated with the accumulation of ORMV or TuMV in a given
tissue. The genes with altered expression profiles in leaves appear to be distinct from those in flowers. In a second approach,
a GFP-tagged virus was used to dissect fluorescent infection foci into four zones expanding out from the center. RNA
from each zone was labeled and hybridized to A. thaliana ATH1 GeneChips. Differential patterns of expression were
observed for over 500 genes that were dependent on virus treatment. The degree to which the expression of these genes
was modulated was largely dependent on the relative accumulation of TuMV in each zone, indicating that most effects on
host gene expression were cell autonomous. Interestingly, TuMV induced many ribosomal proteins and several components
of the 20S core proteasome suggesting that the balance of protein synthesis and turn over is an important component of
the host response. Down-regulated genes related to chloroplast functions or cell wall extensibility were also identified
and suggest potential mechanisms for TuMV-induced symptoms in A. thaliana plants. Other kinds of plant-pathogen
interactions also involve localized interactions between microbes and cells of their hosts, and thus, we expect that the
dissection strategy employed here should be effective for studying events associated with the hypersensitive response
or compatible interactions between plants and bacterial or fungal pathogens as well as other viruses.