Abstract
Tomato (Lycopersicon esculentum Mill.) plants, which normally do not accumulate glycinebetaine (GB), are susceptible to chilling stress. Exposure to temperatures below 10℃ causes various symptoms of injury, and greatly decreases fruit set (i.e., the number of fruits per plants) in most cultivars. Conventional breeding efforts have failed to produce cultivars with satisfactory cold tolerance. Therefore, we have transformed tomato (cv. Moneymaker) with the cod A. gene of Arthrobacter globiformis, which encodes choline oxidase to catalyze the conversion of choline to GB. These transgenic plants express the cod A gene and synthesize choline oxidase, while accumulating up to 0.23μmol of GB per gram fresh weight in their leaves. During various phases of growth and development, from seed germination to fruit production, the GB-accumulating plants are more tolerant of chilling stress than their wild-type counterparts. Moreover, at the reproductive stage, our transgenic tomato plants yield, on average, 30% more fruit after an episode of chilling stress. We demonstrate here that introducing the biosynthetic pathway of GB into tomato via metabolic engineering is an effective strategy for improving fruit production under cold-stress conditions.
