The plastid ω-3 fatty acid desaturase (FAD7) catalyzes the conversion of linoleic acid to linolenic acid. Wounding enhances the expression of the FAD7 gene in leaves and induces its expression in stems and roots. The wound- induced expression of the FAD7 promoter was investigated in transgenic tobacco plants carrying the - 825 Arabidopsis FAD7 promoter::β-glucuronidase (GUS) fusion gene. The protein kinase inhibitor, staurosporine, and the protein phosphatase inhibitor, calyculin A, suppressed the wound induction of the FAD7 gene in stems. A tobacco mitogen-activated protein kinase (WIPK) was rapidly activated upon wounding not only in leaves but also in stems and roots, indicating that WIPK probably mediates the wound signals in most vegetative organs. The FAD7 promoter::GUS fusion gene was introduced into the transgenic tobacco plants in which the wipk gene was expressed constitutively at a high level or into the transgenic plants in which the wipk gene was suppressed possibly due to the transgene-induced gene silencing. The wound- induced expression of the FAD7 gene in stems was enhanced in the former transgenic tobacco plants and suppressed in the latter plants. These results suggest that the wound activation of the FAD7 promoter depends on both protein phosphorylation and dephosphorylation events especially in stems, and also that WIPK is involved in such signaling cascades. (C) 2000 Elsevier Science Ireland Ltd.
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