Fruit-specific lipoxygenase suppression in antisense-transgenic tomatoes

To determine the importance of the enzyme lipoxygenase (LOX) in the generation of volatile C6 aldehyde and alcohol flavour compounds, two antisense LOX genes were constructed and transferred to tomato plants. The first of these constructs (p2ALX) incorporated the fruit-specific 2A11 promoter [Van Haaren, M.J.J., Houck, C.M., 1993. A functional map of the fruit-specific promoter of the tomato 2A11 gene. Plant Mol. Biol. 21, 625-640] and a 1.2 Kb antisense fragment of the cDNA of PTL1 (TomloxA) [Ferrie, B.J., Beaudoin, N., Burkhart, W., Bowsher, C.G., Rothstein, S.J., 1994. The cloning of two tomato lipoxygenase genes and their differential expression during tomato fruit ripening. Plant Physiol. 106, 109-118]; no terminator was included. The second construct (pPGLX) consisted of the ripening-specific polygalacturonase (PG) promoter and terminator [Nicholass, F.J., Smith, C.J.S., Schuch, W., Bird, C.R., Grierson, D., 1995. High levels of ripening-specific reporter gene expression directed by tomato fruit polygalacturonase gene-flanking regions. Plant Mel. Biol. 28, 423-435] and a 400 bp antisense fragment of the tomato cDNA of PTL1 (TomloxA). Both constructs included the highly conserved LOX region (approximately 110 bp) shared by all plant and mammalian lipoxygenase genes. Reduced revels of endogenous TomloxA and TomloxB mRNA (2-20% of wild-type) were detected in transgenic fruit containing the p2ALX construct compared to non-transformed plants, whereas the levels of mRNA for a distinct isoform, TomloxC, were either unaffected or even increased. The pPGLX construct was much less effective in reducing endogenous LOX mRNA levels. In the case of the p2ALX plants, LOX enzyme activity was also greatly reduced compared with wild-type plants. Analysis of flavour volatiles, however, indicated that there were no significant changes. These findings suggest that either very low levels of LOX are sufficient for the generation of C6 aldehydes and alcohols, or that a specific isoform such as TomloxC, in the absence of TomloxA and TomloxB, is responsible for the production of these compounds. (C) 1999 Elsevier Science B.V. All rights reserved.