Molecular Cloning and Characterization of A Novel 1-Aminocyclopropane-1-carboxylate Oxidase Gene Involved in Ripening of Banana Fruits

Abstract

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.

Cloning and characterization of ACC oxidase genes from tulip

“…This organization, including the location of the exon/intron junction, is also identical to the other plants, whereas TgACO5 consisted of three exons interrupted by two introns (data not shown). The same organization was found in CmACO2 of melon and MhACO1 of banana (Lasserre et al 1996;Do et al 2005). This result supports the idea that ACO subfamilies belong to two different clusters, and that tulip ACO genes also belong to these clusters.…”

“…The amino acid sequence of clones TgACO1-4 showed approximately 80% similarity with the other plant ACO clones such as petunia, while the amino acid sequence of TgACO5 showed less than 70% identity. The best score found for TgACO5 is 70% identity with banana MhACO1 (Do et al 2005). Among the tulip ACO proteins, TgACO1-4 share high similarity (90-94% identity); TgACO1 and TgACO3 especially are highly similar (94% amino acid identity).…”

“…Recently, Do et al (2005) have suggested that this alanine is not required for ACO activity. Therefore, each tulip ACO protein might possess the enzyme activities required for ethylene synthesis.…”

Global Transcriptomic Analysis of Targeted Silencing of Two Paralogous ACC Oxidase Genes in Banana

“…Banana MA-ACS1 mRNA accumulated at the onset of the climacteric period, and MA-ACO1 gene encoding banana ACC oxidase was detectable at the preclimacteric stage, then elevated throughout the final stage in the climacteric and postclimacteric phase [26,27]. Similarly, two ACC oxidase genes, Mh-ACO1 (GenBank accession number AF030411) and Mh-ACO2 (GenBank accession number U86045, MA-ACO1 paralog), were found to be involved in banana fruit ripening [28]. Gene expression of Mh-ACO1 was greatly induced at an early stage of fruit ripening in pulp and showed maximal expression at stage 6 [28].…”

“…Similarly, two ACC oxidase genes, Mh-ACO1 (GenBank accession number AF030411) and Mh-ACO2 (GenBank accession number U86045, MA-ACO1 paralog), were found to be involved in banana fruit ripening [28]. Gene expression of Mh-ACO1 was greatly induced at an early stage of fruit ripening in pulp and showed maximal expression at stage 6 [28]. The expression of Mh-ACO2 gene in banana begins after the onset of ripening (stage 2) and continues into later stages of the ripening process [16].…”