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

285 Screening for Suppressors of Arabidopsis acd11
Frederikke Malinovsky 1 , Peter Brodersen 2 , Daniel Hofius 1 , Lea McKinney 1 , Nikolaj H Petersen 1 , Morten Petersen 1 ,
Berthe Fiil 1 , John Mundy 1
1
institue of molecular biology, university of copenhagen, 2 Institut de Biologie Moleculaire des Plantes du CNRS
Despite attempts to link plant cell death to animal apoptosis, comparative analyses of the genetic determinants of
programmed cell death (PCD) in plants and animals have yet to identify conserved gene functions. Loss of function of
the Arabidopsis gene Accelerated Cell Death 11 (ACD11; Brodersen et al. 2002 Genes & Develop. 16, 490; Brodersen
et al. 2005 Plant Physiol. 138, 1037) activates vegetative cell death and disease resistance responses dependent upon the
hormone salicylate (SA). Double mutant analysis showed that of 12 mutants affected in defense-associated PCD (eds1,
pad4, eds5, sid2, npr1, rar1, pbs1, pbs3, ein2, etr1, jar1, ndr1), only two (eds1 and pad4) suppress acd11 PCD in the
presence of the SA analog BTH. To further understand ACD11 function, we are searching for PCD regulators in a largescale
acd11 suppressor screen. More specifically, acd11 homozygotes expressing the bacterial SA hydroxylase nahG were
mutagenized and plants surviving BTH treatment isolated as putative suppressors. This identified a number of recessive
and dominant suppressors of acd11. Recent work has sorted the recessive mutants fall into fifteen complementation
groups. Sequencing has confirmed that two of these groups are allelic to eds1 validating the utility of the screen.
286 Analysis of a nonpathogenic strain of Pseudomonas syringae for use in host range and
pathogenicity studies on Arabidopsis thaliana and tomato
Toni Mohr 1 , Ryan Anderson 1 , Peter Bowerman 1 , Nina Long 1 , Leiya Williams 1 , Joanna Jelenska 2 , Jose Castillo 2 , Jean
Greenberg 2 , Boris Vinatzer 1
1
Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State
University, Fralin Biotechnology Center, West Campus Drive, Blacksburg, VA 24061-0346, USA, 2 Department
of Molecular Genetics and Cell Biology, The University of Chicago, 1103 East 57th Street, EBC410, Chicago, IL
60637, USA
The bacterial plant pathogen Pseudomonas syringae encompasses over 50 pathovars that collectively cause disease
on hundreds of plant species. However, any particular strain is limited to one or a few plant hosts. This host range is
determined by numerous bacterial effector proteins, which are injected into a plant cell by a Type III secretion system
(TTSS). We are examining how TTSS effector proteins affect the host range of Arabidopsis and tomato pathogens. Here
we characterize a nonpathogenic strain, Psy508, originally isolated as a biocontrol strain against the apple scab fungus.
Although closely related to the bean pathogen PsyB728a, Psy508 is unable to cause disease on any tested plant species.
Interestingly, Psy508 does not appear to have a functional TTSS, which is essential for pathogenicity. The typical P.
syringae hrp/hrc cluster with flanking effector loci coding for the TTSS machinery and effectors is absent in this strain,
and has been replaced by a bacteriophage sequence. Additionally, Psy508 appears to be missing most effector genes
elsewhere in the genome. We also sequenced three genomic islands that contain effectors in PsyB728a; these islands are
either rearranged, or lack effector genes in Psy508. Psy508 may thus be a useful strain in which to study the effects of
individual effectors, or combinations of effectors, isolated from other strains with different host ranges. We are currently
cloning the TTSS, without the flanking effector loci, from PsyB728a. By adding this TTSS and individual effectors to
Psy508, we plan to analyze the role of effector proteins in determining the host range of Pseudomonas syringae.