TABLE CONTENTS

TOPIC TEN – HOST PLANT RESISTANCE AND GENETIC MARKERS
DEVELOPMENT
Identifying Members of Mi-DS4 Mediated Hypersensitive Response in
Nicotiana benthamiana using VIGS
Mantelin, S. & I. Kaloshian
Department of Nematology, University of California, Riverside, CA 92521, USA.
Although resistance conferred by the Mi-1 gene has proven to be highly effective for rootknot
nematode (Meloidogyne spp.) control in tomato, the signalling and defensive pathways
required for resistance are largely unknown. Recent development of virus-induced gene
silencing (VIGS) technology allows assessment of the functional role of genes by targeting
their transcripts for degradation. To identify new candidate genes involved in Mi-1-mediated
resistance, we have undertaken a large-scale screen of a cDNA library related to plant
pathogen defense using tobacco rattle virus-based VIGS in Nicotiana benthamiana. The Mi-
1-mediated resistance in tomato is partly characterized by a hypersensitive response (HR),
consisting of localized cell death. Transient expression of Mi-DS4 construct, a constitutive
active form of Mi-1, in N. benthamiana leaves induces HR as well, which was used to
phenotype the silenced plants. To decipher whether the absence of HR was specifically
related to Mi-DS4-mediated HR and not caused by the silencing of a gene involved in the cell
death process itself, we also transiently expressed a constitutive active form of another
resistance gene (Pto) that mediates HR in N. benthamiana. This system has allowed us to
examine so far 2,000 clones identifying about 2% new candidates involved specifically in Mi-
DS4-mediated HR. Further analysis of homologues of these candidates in tomato will provide
insights into the Mi-1-mediated signaling leading to nematode resistance.
GM-crop Impact Assessment on Soil Ecosystems by DNA Barcode-based
Monitoring of Nematode Communities (ERGONema)
De Goede, R. (1), J. Helder (1), E. Hoffland (1), C. Mulder (2) & L. Posthuma (2)
(1) Department of Soil Quality, WUR, Box 47, Wageningen 6700AA, The Netherlands; (2) Ecological Risk
Assessment, RIVM, Box 1, Bilthoven, 3720BA, The Netherlands
Based on the recommendation of the Dutch Advisory commission on Genetic Modification
(Cogem), the Dutch government initiated a research programme (Ecology Regarding Genemodified
Organisms; ERGO) on the better ecological understanding of non-target effects of
genetically-modified (GM) crops on soil ecosystem functioning. We will study such effects
for the interactions between GM-crops, nematodes and soil fertility in our ERGONema
project, starting 2008. The closest interactions between any crop and its environment take
place in the rhizosphere and during litter decomposition. A potentially relevant hazard
scenario is that GM-crops affect organisms, with consequences for soil fertility. Nematodes
constitute a diverse group within the soil fauna, feeding on bacteria, fungi, other nematodes
and plant-roots. This intimate feeding relationship with all major players in direct contact
with plant residues implies that GM-crop effects in the rhizosphere and on the decomposer
community will be reflected in the nematode community. However, for large scale ecological
analysis of communities non-morphological characteristics should be used. DNA barcodes
5 th International Congress of Nematology, 2008 243