Ethylene-regulated expression of ACC oxidase and ACC synthase genes in mung bean hypocotyls

Ethylene induces an increase in transcript levels of the ACC oxidase gene (VR-ACO1) but suppresses expression of the ACC synthase gene (VR-ACS1) in etiolated mung bean hypocotyls. Here, treatment with either the transcription inhibitor α-amanitin or the protein synthesis inhibitor cycloheximide (CHI) completely abolished ethylene-induced accumulation of VR-ACO1 mRNA. This indicated that ethylene-induction of VR-ACO1 is due to transcriptional activation, which also relies on de novo protein synthesis. In contrast, CHI induced the accumulation of VR-ACS1 transcripts. ABA also inhibited ethylene-induced VR-ACO1 expression, but restored ethylene-suppressed VR-ACS1 expression. Results of time-course experiments and an interaction analysis of CHI and ABA suggested that the latter may exert its effect by preventing the synthesis of a factor(s) necessary for ethylene action. Ethylene-signaling was studied in more detail, using two pharmacological inhibitors - EGTA and sodium orthovanadate. Those experiments demonstrated that calcium ions and a Tyr type of protein phosphatase may be involved in regulating ethylene biosynthetic genes.