Molecular cloning and characterization of a novel 1-aminocyclopropane-1-carboxylate oxidase gene involved in ripening of banana fruits

One novel banana fruit ripening related 1-aminocyclopropane-1-carboxylate (ACC) oxidase gene quite different from ACC oxidase genes from other species was cloned. In contrast to other studies, the polypeptide encoded by this gene, named Mh-ACO1, lacks the putative leucine zipper motif which is conserved in all known ACC oxidases including the other previously reported banana ACC oxidase, Mh-ACO2. The Mh-ACO1 locus consists of two nearly identical paralogous ACC oxidase genes arranged in opposite orientation and separated by a 3.1-kb intergenic region. The Mh-ACO1 has only two introns, at positions identical to Mh-ACO(2), which comprises a coding region interrupted by three introns. The predicted amino acid sequence of Mh-ACO1 shares less than 50% identity to those of ACC oxidase from other climacteric fruits, while that of Mh-ACO(2) shows more than 65% homology. When expressed in Saccharomyces cerevisiae Mh-ACO1-encoded protein possessed the enzyme activity for ethylene conversion, The levels of mRNA corresponding to both Mh-ACO1 and Mh-ACO2 increased during fruit ripening and were induced by exogenous ethylene. We conclude that both Mh-ACO1 and Mh-ACO2 contribute to increased ethylene production in fruits and these two genes are differentially expressed in fruits and other organs in banana.