Phytohormones have been known for decades to modulate plant development; however, the molecular mechanisms involved are only beginning to be discovered. Although not well understood, several lines of evidence suggest considerable interplay and crosstalk among various phytohormones for the modulation of plant growth. Morphological and biochemical evidence have shown that local phytohormone levels and hormone response pathways are altered in nematode-infected roots and may play a significant role in nematode feeding site (NFS) formation. We have characterized a tobacco endo-ß-1,4-glucanase gene promoter (NtCel7) that it is upregulated within nematode feeding sites during the early stages of their formation and is responsive to auxin. Phytohormones imbalances induced by nematodes likely result in altered expression of cell wall modifying enzymes with a central role in the controlled cell wall architechural modifications observed during feeding cell development. Several other hormone-responsive plant gene promoters have been shown to be upregulated in NFS and both auxin and ethylene-insensitive mutants are less susceptible to cyst nematodes due to impairments in feeding cell development. It is not entirely clear whether the nematode produces plant hormones for secretion into plant cells, or modulates the level of host phytohormone levels by affecting transport or redirecting normal plant biosynthetic and signaling pathways. We are using the model plant, Arabidopsis thaliana, as a parallel system to dissect the complex plant-nematode interaction. We are interested in elucidating how the nematode alters the complex plant hormone biosynthetic and signaling networks for the development of nematode feeding sites in plant roots. This involves studying the expression and function of genes encoding biosynthetic and catabolic enzymes, hormone signaling pathway components, and response genes in both model plants and soybean.