Abolition of an Inducible Highly Anionic Peroxidase Activity in Transgenic Tomato.

Locally induced expression of a highly anionic peroxidase has previously been correlated temporally and spatially with suberization of tissues responding to pathogen assault, wounding, or exogenously applied abscisic acid or fungal elicitors. DNA sequences corresponding to the 5[prime] regions of two tomato (Lycopersicon esculentum) genes encoding homologous anionic peroxidases were fused, inserted into a pTi-based plasmid designed to express a composite antisense transcript, and introduced into tomato via Agrobacterium-mediated transformation. RNA gel-blot analyses showed high expression of the antisense transcript in most transgenic plants and no detectable induction of native anionic peroxidase transcripts in wounded or abscisic acid or pathogen-treated tissues. Plants and fruits expressing the antisense transcript appeared normal in all respects. Electrophoretic analysis of anionic proteins from selected transgenic plants showed no detectable anionic peroxidase protein or activity. Depolymerization of polymeric material from the wound periderm of transgenic tomato fruits and analysis of the aliphatic products by gas-liquid chromatography/mass spectrometry showed that the content and composition of C16/C18 [omega]-hydroxy and dicarboxylic acids, characteristic of suberin, were not affected by the absence of the anionic peroxidase. Autofluorescence generated from cell wall phenolics at the wound lesion was also not affected by the absence of the highly anionic peroxidase.