**3. Conclusions**

Soybean genes involved in glycolysis/gluconeogenesis are up-regulated during nematode feeding and several lines of evidence indicate that the gluconeogenesis is occurring. This would allow soybean cells to provide carbohydrates as an energy source to the nematode. Genes encoding enzymes involved in cell wall molding are up-regulated, including cellulases, pectinesterases and xyloglucanases. These increases in gene expression allow the development and expansion of the syncytium for nematode feeding. Genes encoding important enzymes involved in the synthesis of jasmonic acid are down-regulated in the compatible interaction. This would quench the defense response controlled by jasmonic acid and related compounds and allow the nematode to grow and develop in a compatible reaction. In general, genes encoding pathogenesis-related proteins are more highly expressed in the incompatible interaction and a gene encoding phenylalanine ammonia lyase is much more highly expressed in the incompatible interaction of soybean roots with SCN. Phenylalanine ammonia lyase is major gateway to phenylpropanoid metabolism and to the synthesis of numerous secondary compounds involved in plant defense, All of these data indicate that there is a stronger production of transcripts of genes encoding proteins involved in the plant defense response in the incompatible interaction, while transcripts of many of these genes are lower or the genes are down-regulated leading to a weaker defense response in the compatible reaction of soybean roots to SCN. Gene expression studies performed in soybean has resulted in the understanding gene expression during infection by SCN. The challenge to scientists now is in testing the function genes to understand the molecular circuitry occurring between plants and their parasitic nematodes so new methods of nematode control can be developed.
