Towards the production of transgenic pineapple to control flowering and ripening

In Queensland, pineapple plants are artificially induced to flower by spraying with chemical agents as a standard industry practice; nevertheless an important percentage of plants flower naturally with fruit maturing ahead of the normal summer harvest. This results in the need of extra harvest passes and significantly increases growing costs. In pineapple, ethylene is thought to be responsible for natural flowering due to low temperatures. ACC synthase is the key regulatory enzyme in the biosynthesis of ethylene. Our research team has isolated and characterised an ACC synthase gene induced by cold temperature treatment of pineapple plants followed by an extended warm period. We are producing transgenic pineapple plants carrying sense and antisense copies of the flowering-related ACC synthase gene in order to down-regulate the expression of the gene and therefore suppress natural flowering. Pineapples are not climacteric fruits but nevertheless ethylene is believed to play a significant role during ripening. Important quality traits such as skin texture and colour are linked to the production of ethylene by the fruit. To this aim we have studied pineapple fruit ripening as our model system. We have cloned and characterised several ACC synthase and ACC oxidase genes and have shown for the first time that the two key genes involved in ethylene biosynthesis are induced during pineapple fruit ripening. Transgenic plants containing sense and antisense copies of the ripening-related ACC synthase gene are being produced. We expect to study the effects of suppression of internal ethylene in the transgenic fruits.