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

Root-knot and cyst nematodes are obligate plant parasites that induce compl ex biotrophic feeding structures in host roots. The mechanisms by which nem atodes regulate host gene expression to produce feeding sites are unknown. The cauliflower mosaic virus (CaMV) 35S promoter has been reported to be re pressed strongly in the feeding sites of both root-knot and cyst nematodes. In contrast, other work has indicated that this promoter is partially acti ve in some feeding sites. Considering the importance of the 35S promoter in biotechnology, we have defined the nematode-responsive nature of this prom oter in more detail. Transgenic tobacco harboring various 35S-uidA construc ts was assayed for beta-glucuronidase (GUS) activity after infection by roo t-knot nematodes (Meloidogyne incognita) and cyst nematodes (Globodera taba cum subsp, tabacum). The entire 35S promoter (-343 to +8) was active in gia nt 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 fee ding sites matured. Subdomains of the 35S promoter were also active in feed ing sites, particularly B4 and B5 in giant cells. However, subdomain B3 was strongly down-regulated in gall tissue and syncytia, In total, 14 construc ts were studied and nematode-responsive expression was always stronger and more consistent with the root-knot nematode than the cyst nematode.