15th International Conference on Arabidopsis Research - TAIR

T05-053
Genetic dissection of non-host disease resistance to
fungal pathogens in Arabidopsis
Volker Lipka(1, 2), Jan Dittgen(1), Paul Schulze-Lefert(1)
1-Max-Planck Institute for Plant Breeding Research, Dep. of Plant Microbe Interactions, Carl-von-
Linné-Weg 10, 50829 Cologne, Germany
2-ZMBP, Forschungsgruppe Pflanzenbiochemie, Eberhard-Karls-Universität Tübingen, Auf der
Morgenstelle 5, 72076 Tübingen, Germany
Wild-type Arabidopsis is a non-host to the biotrophic barley powdery mildew
fungus, Blumeria graminis f.sp. hordei (Bgh). We identified several Arabidopsis
mutants that are partially compromised in non-host resistance to this
inappropriate powdery mildew species. On these pen (penetration) mutants
(pen1 and pen2), the entry success rate into attacked epidermal cells is
dramatically increased and combined with efficient haustorium formation.
Further fungal growth is however terminated coincident with a cell death
response of haustorium containing cells. Interestingly, pen2 mutant plants
show aberrant interaction phenotypes with multiple different plant pathogen
species (e.g. Phytophthora infestans, Plectospherella cucumerina, Colletotrichum
lagenarium) whereas impaired penetration resistance of pen1 mutants
appears to be restricted to powdery mildew species.
We recently documented the identification of PEN1, which encodes a syntaxin
potentially directing exocytotic vesicle traffic towards sites of attempted
fungal penetration (Collins et al., 2003). Here, we present the identification
of PEN2 which exhibits significant sequence similarity to family 1 ß-glycosyl
hydrolases.
In plants, ß-glycosyl hydrolase activity is involved in processes such as
activation of phytohormones, floral development and pigmentation, defense
mechanisms, lignification and cell wall decomposition. Transgenic complementation
analysis with wt PEN2-cDNA as well as catalytically inactive variants
revealed that catalytic activity is required for PEN2 function in non-host
resistance. First results from comparative metabolic profiling experiments
aiming at the identification of the in planta substrate(s) of PEN2 will be
presented.
To assess the contribution of already described defence components to Arabidopsis
non-host resistance we generated a collection of pen2 double/triple
mutant combinations and analyzed their interaction phenotypes with Bgh and
another inappropriate fungal pathogen, the pea powdery mildew Erysiphe pisi
(Ep). Despite a significant increase of secondary hyphal growth on particular
double mutant lines, Bgh was still unable to complete its asexual life-cycle
by sporulation. In marked contrast, the same double mutant combinations
supported growth and sporulation of Ep, suggesting that inactivation of least
two defence layers is sufficient to make Arabidopsis a host for Ep but not for
Bgh. The conceptual implications of these findings will be discussed.
Collins et al. (2003) SNARE protein mediated disease resistance at the plant cell wall. Nature 425:
973-977
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T05-054
A new Myrosinase gene family in Arabidopsis
thaliana
Derek Andersson(1), Romit Chakrabarty(1), Jiaming Zhang(2), Johan Meijer(1)
1-Dept. of Plant Biology and Forest Genetics, Box 7080, Swedish University of Agricultural
Sciences, SE-75007 Uppsala, Sweden
2-National Key Biotechnology Laboratory for Tropical Crops, CATAS, Chengxi, Haikou, Hainan,
China
Myrosinases (EC 3.2.3.1), catalyse hydrolysis of the secondary metabolites
glucosinolates into various toxic products to prevent pest damage. This
binary system is present in Capparales and different species have evolved to
contain a unique blend of different glucosinolates and several myrosinases
that provides a chemical barrier to most pests as well as to serve in plant
development. We are studying myrosinase genes in Brassicas in comparison
with Arabidopsis thaliana. Gene scanning of the Arabidopsis genome using
conserved features of known myrosinase genes in combination with preliminary
biochemical studies suggested the presence of six myrosinase genes
TGG1 - TGG6 in Arabidopsis. These genes are organized into two subgroups
consisting of TGG1-TGG3 (on chromosome 1) and TGG4-TGG6 (on chromosome
5), respectively. While TGG4 and TGG5 are almost identical and >60%
sequence identities occur between earlier known myrosinase genes, the
sequence identities between the Arabidopsis two myrosinase gene groups
are