Towards Transformation, Regeneration and Screening of Papaya Containing Antisense ACC Synthase Gene

Abstract

The papaya (Carica papaya L.) is usually being harvested when they are about 25% ripe or when a tinge of yellow color appears on the skin. It takes only one to two weeks before the fruit ripens completely from the time of harvest. Losses due to postharvest diseases in some species reach up to about 60% of annual production. The two most important qualities required for efficient marketing of fruits are the taste and the overall appearance. The flexibility in marketing is determined mainly by the rate of fruit ripening. An extended ripening phase would prolong its shelf-life, thus allowing the fruit to be shipped to distant markets without spoilage, thereby increasing the potential target markets, and enabling the fruit to reach the market in better condition. The papaya is a climacteric fruit and ripening is in part, being controlled by the simple hydrocarbon ethylene. The rate-limiting enzyme of the ethylene biosynthetic pathway is ACC synthase. This enzyme has been the target in engineering the ethylene biosynthesis pathway using the antisense technology. This technology for instance has been used to reduce translation of either ACC synthase or ACC oxidase by antisense RNA that blocks ethylene production in tomato, thereby delaying fruit ripening (Oeller et al., 1991; Hamilton et al., 1991). Two ACC synthase genes expressed during fruit ripening have been cloned from papaya (Mason and Botella, 1997). These genes could be used for transforming papaya plants that could constitutively express an antisense copy of the ACC synthase gene. In this study, we aimed to apply antisense technology and the existing transformation protocol to produce transgenic Solo papayas.