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

275 Protein Prenylation Is Required In Plant Innate Immunity
Sandra Goritschnig 1 , Yuelin Zhang 2 , Xin Li 1
1
Michael Smith Laboratories and Dept. of Botany, University of British Columbia, Vancouver, Canada,
2
National Institute of Biological Sciences, Beijing, People's Republic of China
Plant defenses toward invading pathogens involve intricate signaling networks that fine-tune physiological responses in the
infected cells to limit pathogen spread while minimizing harmful effects on the rest of the plant. Specific resistance responses
are mediated by Resistance (R-) proteins that recognize pathogen-derived molecules and initiate signaling cascades culminating
in a successful resistance response.
We use a unique gain-of-function R-gene mutant, snc1, as a tool to identify and study components of resistance signaling
in Arabidopsis. In snc1 a point mutation in an RPP5 homolog causes constitutive expression of pathogenesis-related genes and
enhanced resistance to virulent pathogens. In a screen for suppressors of snc1-mediated constitutive resistance, we identified
a number of modifier of snc1 (mos) mutants that reveal roles for nucleo-cytoplasmic trafficking (1, 2) and RNA metabolism
(3) in defense signaling.
Here, we present mos8, another suppressor of snc1 that completely disrupts resistance against virulent bacterial and oomycete
pathogens. mos8 was found to be allelic to enhanced resistance to abscisic acid 1 (era1), a mutant in the beta-subunit of plant
farnesyltransferase, which was first described based on phenotypes correlating with ABA signaling, including germination and
stomatal closure. era1 mutants also have enlarged meristems and flower defects, indicating a role for prenylation in meristem
identity.
mos8 and other era1 alleles show enhanced susceptibility to several virulent pathogens, indicating a requirement for
prenylation in basal resistance. Responses to avirulent pathogens are partially affected in mos8, further suggesting the existence
of highly divergent and pathogen-specific signaling pathways, some of which require prenylated proteins. Using mos8 and
a reverse genetics approach we are addressing potential functions for prenylated proteins in plant resistance signaling. Our
research provides insight into novel aspects of the interplay between protein modification and resistance signaling pathways.
1) Palma et al. (2005) Curr Biol 15, 1129-1135;
2) Zhang and Li (2005) Plant Cell 17, 1306-1316;
3) Zhang et al. (2005). Curr Biol 15, 1936-1942.
276 A toolkit allowing induction of IAA and indole glucosinolate production in planta
Bjarne Hansen, Jing LI, Ida Soenderby, Niels Jensen, Barbara Halkier
Department of Plant Biology, Plant Biochemistry laboratory, KVL, Copenhagen, Denmark
Characteristic for the cruciferous plants, which include Arabidopsis, is the content of a variety of sulphur-rich indole
compounds, such as e.g. indole glucosinolates and indole alkoloids, e.g. camalexin in Arabidopsis. These compounds are
known to play a role in plant defence either as constitutively expressed phytoanticipines or as pest-inducible phytoalexins.
Furthermore, the breakdown product of specific glucosinolates has been shown to exhibit surprisingly potent but welldocumented
cancer-preventive properties.
Recent findings have demonstrated that IAOx constitutes an important branching point between the biosynthetic
pathway of indole glucosinolates, IAA, and camalexin in the model plant Arabidopsis.
We have reintroduced CYP79B2 under the control of the ethanol-inducible promoter AlcA in a cyp79B2/cyp79B3
double knockout and in a cyp79B2/cyp79B3/cyp83B1 triple knockout mutant, which allows the control of IAOx
biosynthesis. The control of IAOx production has been found to be very tight with no IAOx production in the absence
of ethanol and a high level of IAOx production after ethanol treatment. The two genetic backgrounds allow the induction
of either indole glucosinolate or IAA production. This provides a powerful system for investigating the role of indole
glucosinolates and camalexin in plant defence. Furthermore, it provides a system that allows the use of microarray for
gene discovery of auxin responsive genes and IAOx-metabolizing enzymes as these plants are morphological identical
before treatment with ethanol.
Premilinary microarray data show that CYP79B2 and known auxin responsive genes are among the most upregulated
genes after ethanol treatment.