Expression characteristics of CS-ACS1, CS-ACS2 and CS-ACS3, three members of the 1-aminocyclopropane-1-carboxylate synthase gene family in cucumber (Cucumis sativus L.) fruit under carbon dioxide stress

Fire investigated the expression pattern of three 1-aminocyclopropane-1-car boxylate (ACC) synthase genes, CS-ACS1, CS-ACS2 and CS-ACS3 in cucumber (Cu cumis sativus L.) fruit under CO2 stress. CO2 stress-induced ethylene produ ction paralleled the accumulation of only CS-ACS1 transcripts which disappe ared upon withdrawal of CO2. Cycloheximide inhibited the CO2 stress-induced ethylene production but superinduced the accumulation of CS-ACS1 transcrip t. At higher concentrations, cycloheximide also induced the accumulation of CS-ACS2 and CS-ACS3 transcripts. In the presence of CO2 and cycloheximide, the accumulation of CS-ACS2 transcript occurred within Ih, disappeared aft er 3h and increased greatly upon withdrawal of CO2. Inhibitors of protein k inase and types 1 and 2A protein phosphatases which inhibited and stimulate d, respectively, CO2 stress-induced ethylene production had little effect o n the expression of these genes. The results presented here identify CS-ACS 1 as the main ACC synthase gene responsible for the increased ethylene bios ynthesis in cucumber fruit under CO2 stress and suggest that this gene is a primary response gene and its expression is under negative control since i t is expressed by treatment with cycloheximide. The results further suggest that the regulation of CO2 stress-induced ethylene biosynthesis by reversi ble protein phosphorylation does not result from enhanced ACC synthase tran scription.