A cDNA encoding the banana 1‐aminocyclopropane‐l‐carboxylate (ACC) oxidase has previously been isolated from a eDNA library that was constructed by extracting poly(A)+ RNA from peels of ripening banana. This cDNA, designated as pMAO2, has 1,199 bp and contains an open reading frame of 318 amino acids. In order to identify ripening‐related promoters of the banana ACC oxidase gene, pMAO2 was used as a probe to screen a banana genomic library constructed in the λEMBL3 vector. The banana ACC oxidase MA02 gene has four exons and three introns, with all of the boundaries between these introns and exons sharing a consensus dinucleotide sequence of GT‐AG. The expression of MA02 gene in banana begins after the onset of ripening (stage 2) and continues into later stages of the ripening process. The accumulation of MAO2 mRNA can be induced by 1 μl/l exogenous ethylene, and it reached steady state level when 100 μl/1 exogenous ethylene was present.

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 locus consists of two nearly identical paralogous ACC oxidase genes arranged in opposite orientation and separated by a 3.1-kb intergenic region. The has only two introns, at positions identical to , 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-ACO2 shows more than 65% homology. When expressed in Saccharomyces cerevisiae -encoded protein possessed the enzyme activity for ethylene conversion. The levels of mRNA corresponding to both and increased during fruit ripening and were induced by exogenous ethylene. We conclude that both and contribute to increased ethylene production in fruits and these two genes are differentially expressed in fruits and other organs in banana.