Fruit-specific lipoxygenase suppression in antisense-transgenic tomatoes

To determine the importance of the enzyme lipoxygenase (LOX) in the generat ion of volatile C6 aldehyde and alcohol flavour compounds, two antisense LO X genes were constructed and transferred to tomato plants. The first of the se constructs (p2ALX) incorporated the fruit-specific 2A11 promoter [Van Ha aren, M.J.J., Houck, C.M., 1993. A functional map of the fruit-specific pro moter of the tomato 2A11 gene. Plant Mol. Biol. 21, 625-640] and a 1.2 Kb a ntisense 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 to mato lipoxygenase genes and their differential expression during tomato fru it ripening. Plant Physiol. 106, 109-118]; no terminator was included. The second construct (pPGLX) consisted of the ripening-specific polygalacturona se (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 r egions. Plant Mel. Biol. 28, 423-435] and a 400 bp antisense fragment of th e tomato cDNA of PTL1 (TomloxA). Both constructs included the highly conser ved LOX region (approximately 110 bp) shared by all plant and mammalian lip oxygenase genes. Reduced revels of endogenous TomloxA and TomloxB mRNA (2-2 0% of wild-type) were detected in transgenic fruit containing the p2ALX con struct compared to non-transformed plants, whereas the levels of mRNA for a distinct isoform, TomloxC, were either unaffected or even increased. The p PGLX construct was much less effective in reducing endogenous LOX mRNA leve ls. In the case of the p2ALX plants, LOX enzyme activity was also greatly r educed compared with wild-type plants. Analysis of flavour volatiles, howev er, indicated that there were no significant changes. These findings sugges t that either very low levels of LOX are sufficient for the generation of C 6 aldehydes and alcohols, or that a specific isoform such as TomloxC, in th e absence of TomloxA and TomloxB, is responsible for the production of thes e compounds. (C) 1999 Elsevier Science B.V. All rights reserved.