Plant & Animal Genome VI Conference

W84

DIFFERENTIALLY EXPRESSED GENES OF SOYBEAN IN RESPONSE TO INVASION BY THE SOYBEAN CYST NEMATODE

USDA ARS, Soybean and Alfalfa Research Laboratory, Beltsville, MD 20705

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe is a devastating pest of the soybean, Glycine max L Merr. worldwide and is responsible for millions of dollars worth of damage. SCN Infection of soybean causes chlorosis, root necrosis, and suppresses shoot growth. We examined the differential expression of genes in resistant and susceptible soybean cultivars during invasion by soybean cyst nematode, race 3. Using differential display we identified genes induced in leaf and roots of resistant and susceptible plants 6, 12, 24, 48, 96 and 144 hours after inoculation with SCN. More than 50 bands were cloned and their ends were sequenced. These represented genes expressed in the resistant inoculated plant but not in the susceptible, uninoculated or wounded control plants. The DNA sequences were compared against nucleotide and protein sequence databases to identify possible homologues from other systems. Differentially expressed genes appeared at early (6-24 hours), intermediate (24-48 hours) or late (48-144 hours) stages of the nematode infection process. In the early stage coinciding with nematode penetration and migration through the root, the genes detected were involved in regulation of gene expression. These included transcription factors and different nucleotide binding proteins. During the intermediate period of the infection, the initial feeding site is selected. Some regulatory genes are still differentially expressed. Also general defense response genes such as chitinases and peroxidases are turned on. The late stage of the infection process correlates with syncytial establishment in the susceptible plant or syncytial degeneration in the resistant plant. At this time a massive induction of general defense response genes occurs, as peroxidases, chitinases, and heat shock proteins are turned on. Identifying and understanding the function of genes expressed throughout the nematode infection process may clarify the events taking place and aid scientists in designing new modes of resistance.