REDUCED ETHYLENE SYNTHESIS BY TRANSGENIC TOMATOES EXPRESSING S-ADENOSYLMETHIONINE HYDROLASE

We have utilized a gene from bacteriophage T3 that encodes the enzyme S-adenosylmethionine hydrolase (SAMase) to generate transgenic tomato plants that produce fruit with a reduced capacity to synthesize ethyle ne. S-adenosylmethionine (SAM) is the metabolic precursor of 1-aminocy clopropane-1-carboxylic acid, the proximal precursor to ethylene. SAMa se catalyzes the conversion of SAM to methylthioadenosine and homoseri ne. To restrict the presence of SAMase to ripening fruit, the promoter from the tomato E8 gene was used to regulate SAMase gene expression. Transgenic tomato plants containing the 1.1 kb E8 promoter bore fruit that expressed SAMase during the breaker and orange stage of fruit rip ening and stopped expression after the fruit fully ripened. Plants con taining the 2.3 kb E8 promoter expressed SAMase at higher levels durin g the post-breaker phases of fruit ripening and had a substantially re duced capacity to synthesize ethylene.