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Induction of the Hahsp17.7G4 Promoter by Root-Knot Nematodes: Involvement of Heat-Shock Elements in Promoter Activity in Giant Cells

¹Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Campus de la Real Fábrica de Armas, E-45071 Toledo, Spain; ²Departamento de Biología, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain; ³Instituto de Recursos Naturales y Agrobiología, CSIC, Avenida Reina Mercedes 10, E-41012 Sevilla, Spain

Root-knot nematodes feed from specialized giant cells induced in the plants that they parasitize. We found that the promoter of the Hahsp17.7G4 gene, which encodes a small heat-shock protein involved in embryogenesis and stress responses, directed GUS expression in tobacco galls induced by the root-knot nematode Meloidogyne incognita. In roots containing a GUS reporter fusion to the Hahsp17.7G4 promoter, 10% of the galls stained for GUS expression 1 to 3 days after infection and the fraction stained increased to 60 to 80% 17 to 20 days after infection. A DNA fragment from −83 to +163, which contains heat-shock element (HSE) core sequences, is sufficient to support a promoter activity largely restricted to giant cells within the galls. Two-point mutations in HSE cores, previously reported to abolish the heat-shock response and to strongly reduce the embryogenesis response of the same promoter, did not reduce expression in giant cells. This suggests a distinct regulation of the promoter by nematodes. However, additional point mutations located at positions crucial for binding of heat-shock transcription factors (HSFs) caused a severe decrease in the nematode response. These results demonstrate that HSEs are involved in the promoter activation in giant cells and suggest that HSFs may mediate this response.