Glucuronidase expression in transgenic tobacco roots with a Parasponia promoter on infection with Meloidogyne java']javanica

The expression of a gus reporter gene linked to a Parasponia andersonii hemoglobin promoter has been studied in transgenic tobacco plants after infection by Meloidogyne javanica. Transgenic roots were harvested at different times after nematode inoculation, and stained histochemically for expression of the gus gene. During the early stages of infection (0-2 weeks) there was little expression in giant cells, in contrast to other cells of the root. In later stages of infection (3-6 weeks) there was strong gus expression in giant cells, with virtually no expression in other cells of the root. The Parasponia hemoglobin promoter therefore appears to direct down-regulation of linked genes on induction of giant cells, but up-regulation in mature giant cells. This reflects different metabolic activities in the giant cells depending on their stage of development. The Parasponia hemoglobin promoter may respond to oxygen tension in giant cells. This suggests that oxygen tension may be limited in the metabolically active giant cells that are associated with egg-laying females.