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

Abstract

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 ofVR- ACO1 mRNA. This indicated that ethylene-induction ofVR- ACO1 is due to transcriptional activation, which also relies onde novo protein synthesis. In contrast, CHI induced the accumulation ofVR- ACS1 transcripts. ABA also inhibited ethylene-inducedVR- ACO1 expression, but restored ethylene-suppressedVR- 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.