Modulation of stress-inducible ethylene biosynthesis by sense and antisense gene expression in tobacco

To study the significance of stress-inducible ethylene in the hypersensitive reaction of tobacco (Nicotiana tabacum) to tobacco mosaic virus (TMV), six types of transgenic plants were generated containing sense or antisense constructs corresponding to the ethylene biosynthesis enzymes ACC-synthase (ACS) and/or ACC-oxidase under the control of the CaMV 35S promoter. In most primary transformants, expression of antisense RNA or incomplete sense RNA resulted in a reduction of inducible ethylene production, while plants overexpressing full-length sense ACS mRNA had higher ethylene levels than control plants. Although efficient overexpression or gene silencing was evident at the transcript level, there was no correlation with the amounts of ethylene produced, supporting the notion that ACS is post-transcriptionally regulated. Transgenic tobacco plants with altered ethylene levels were not impaired in their ability to respond with necrotic local lesions to infection with TMV. However, in the ACS sense and antisense transformants, alterations in ethylene levels did affect stem length and leaf chlorophyll levels in accordance with established ethylene responses. (C) 1997 Elsevier Science Ireland Ltd.