cDNA cloning of ACC synthase and ACC oxidase genes in cucumber fruit and their differential expression by wounding and auxin

We cloned and sequenced three cDNA homologs of 1-aminocyclopropane-1-carboxylate (ACC) synthase (pCS-ACS1, pCS-ACS2 and pCS-ACS3) and two of ACC oxidase (pCS-ACO1 and pCS-ACO2) from cucumber (Cucumis sativus L.) fruit using RT-PCR (reverse transcription and polymerase chain reaction) and RACE (rapid amplification of cDNA ends) PCR. Conserved amino acid sequences reported for other plant tissues were found in all the cloned ACC synthase and ACC oxidase cDNAs. Among the ACC synthase and ACC oxidase cDNA clones, pCS-ACS1, pCS-ACS3, and pCS-ACO1 were highly homologous to ACC synthase and ACC oxidase genes cloned from other Cucurbitaceae family at both the nucleotide and the amino acid levels. Northern blot analysis showed that wounding induced the accumulation of CS-ACS1, CS-ACS2, and CS-ACO1 mRNAs, whereas IAA treatment induced expression of all the three ACC synthase genes and CS-ACO1. These expressions paralleled ethylene production in both treatments. Transcripts for CS-ACO2 were constitutively expressed and were not affected by wounding and IAA treatments. From the expression pattern and the sequence similarities of these genes, we conclude that CS-ACS1 could be a wound-inducible gene and that CS-ACS3 is an auxin-inducible one. These results strongly suggest that in cucumber fruit these genes are differentially expressed by wounding and auxin and are involved in the regulation of ethylene biosynthesis at the transcriptional level.