Isolation and characterization of a cDNA encoding an ACC oxidase from Cicer arietinum and its expression during embryogenesis and seed germination

A full length cDNA (caaco1) encoding a putative ACC-oxidase (ACCO) was isolated and sequenced from embryonic axes of chick-pea (Cicer arietinum L.) seeds, which depend on ethylene synthesis for germination. The deduced protein for caaco1 has a molecular weight of 36 kDa, a high homology with other ACCOs and is apparently found in the cytosolic fraction of the cell. Heterologous expression of this cDNA confirmed that the protein product exhibits ACCO activity and a molecular weight close to 38 kDa. Southern blot analysis shows that there are at least two genes encoding ACCO in the chick-pea genome. The caaco1 mRNA levels in seeds remained constant during the initial stages of embryogenesis decreasing in the latest stages. During germination, caaco1 mRNA levels increase, reaching a maximum at 24 h, coinciding with the maximum percentage of germination (when all seeds are germinated), ACCO activity and ethylene production. It is interesting that there is a shift in the tissue source of the caaco1 mRNA during embryogenesis and germination. While the bulk of the expression was detected in cotyledons during embryogenesis, it was the embryonic axis that provided most of the expression detected during germination. Our data suggest that during embryogenesis ACCO is regulated at the translational level, but during germination at the transcriptional level.