Abstract
Ethylene, a gaseous plant hormone regulates essentially all physiological processes during the plant’s life cycle. The practical implications of ethylene biosynthesis regulation for plant improvement have supported the continuous basic research on dissecting the structure of genes encoding ethylene biosynthetic enzymes, their differential expression patterns, and mechanisms underlying their transcriptional activity. ACC oxidase (ACO) is involved in the final step of ethylene production in plant tissues. In various plants several ACO isoforms have been isolated which are encoded by a multigenic family. There is a strong evidence that ACO gene expression is positively correlated to the ethylene production rates and its multiple isoforms are under development and environmental control. Thus, the regulation of ACO gene activity may act either as an additional or in several cases also as a main level for controlling ethylene biosynthesis in higher plants. This review summarizes in detail the knowledge about organization and gene structure, and transcriptional expression of ACO genes from different plant species. The perspectives of manipulating ACO gene as a method in biotechnological modification of ethylene synthesis are also discussed.
Highlights
Ethylene, a gaseous plant hormone regulates essentially all physiological processes during the plant’s life cycle
There is a strong evidence that ACC oxidase (ACO) gene expression is positively correlated to the ethylene production rates and its multiple isoforms are under development and environmental control
Even though ACO gene homologs have been isolated from a number of species, the biochemical properties, in vivo stability, and/or physiological functions of the gene products are in many cases not fully understood
Summary
ACC oxidase is a member of ferrous-dependent nonheme oxygenases, most of which utilize 2-oxoglutarate (2OG) as a co-substrate (Mirica and Klinman 2008). The common ACO gene structure in many different plant species consists of four exons interspersed by three introns (Fig. 3a) The occurrence of such organization has been observed in over 80 % of genes with known sequence of their genomic DNA (Table S1). The coding regions of OS-ACO2 and OS-ACO3 share 92 and 72 % sequence identity at the amino acid level with OS-ACO1, indicating that the OS-ACO3 gene is a more divergent member of the gene family. The other subfamily consists of ZM-ACO15 and ZM-ACO31 which are highly similar to each other (96 % amino acid identity) These two subfamilies have diverged considerably so that a greater degree of divergence is found among members of the maize ACO gene family than that reported for other species such as petunia and tomato (Tang et al 1993; Barry et al 1996). PT-ACO3 has shown to be quite divergent from the first two paralogs in overall gene structure in containing only two introns instead of three
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