Nematode-responsive activity of the cauliflower mosaic virus 35S promoter and its subdomains

Root-knot and cyst nematodes are obligate plant parasites that induce complex biotrophic feeding structures in host roots. The mechanisms by which nematodes regulate host gene expression to produce feeding sites are unknown. The cauliflower mosaic virus (CaMV) 35S promoter has been reported to be repressed strongly in the feeding sites of both root-knot and cyst nematodes. In contrast, other work has indicated that this promoter is partially active in some feeding sites. Considering the importance of the 35S promoter in biotechnology, we have defined the nematoderesponsive nature of this promoter in more detail. Transgenic tobacco harboring various 35S-uidA constructs was assayed for β-glucuronidase (GUS) activity after infection by root-knot nematodes (Meloidogyne incognita) and cyst nematodes (Globodera tabacum subsp. tabacum). The entire 35S promoter (-343 to +8) was active in giant cells induced by M. incognita and, to a lesser extent, the syncytia of G. tabacum subsp. tabacum. In the latter case, activity decreased as the feeding sites matured. Subdomains of the 35S promoter were also active in feeding sites, particularly B4 and B5 in giant cells. However, subdomain B3 was strongly down-regulated in gall tissue and syncytia. In total, 14 constructs were studied and nematode-responsive expression was always stronger and more consistent with the root-knot nematode than the cyst nematode.