**2.3 Plant defense system**

When a nematode invades a plant root, it must repress or control the plant defense response, so it can successfully establish its permanent feeding site (Caillaud *et al*., 2001). These defense responses may include the production of jasmonic acid and salicylic acid, the hypersensitive response, cell wall strengthening, the production of pathogenesis related (PR) proteins, and other cellular defense responses. There are changes in the expression of genes involved in many of these defense responses in both compatible and incompatible interactions of SCN with soybean and with RKN and soybean in the compatible interaction. Many of the same genes are altered in expression in both the compatible and incompatible interaction. However, the amount of change in transcript abundance may be very important and in some cases a gene is up regulated in one interaction and down regulated in another interaction

Fig. 4. (A) Fold change in expression of genes encoding xyloglucanases in syncytia in a compatible interaction (S) at 2, 5 and 10 dai. Data from Ithal. *et al. (*2007b) and (B) an incompatible interaction at 3, 6 and 9 dai Data from Klink *et al*.(2009a). Genes are represented by GenBank numbers.
