Abstract
ACC synthase (ACS), a rate-limiting enzyme of ethylene biosynthesis, is regulated not only transcriptionally but also post-translationally. We previously reported that LeACS2, a wound-inducible ACS in tomato, is immediately phosphorylated after translation and almost all LeACS2 molecules act as phosphorylated form and that the half-life of dephosphorylated LeACS2 is shorter than that of phosphorylated LeACS2. These evidences suggest that dephosphorylation step defines the rate of ACS turnover. Among Arabidopsis mutants which overproduce ethylene, we focused on rcn1 which disrupts a regulatory subunit of protein phosphatase 2A. Auxin treatment induced the expression of AtACS4, followed by ethylene production in etiolated Arabidopsis seedlings. Although the expression levels of AtACS4 mRNA were equivalent between wild-type and rcn1, ACC contents and ethylene production in rcn1 were higher than those in wild-type. Theses results suggest that the elevated level of ethylene production in rcn1 results from the alternation of AtACS4 turnover.
