Tomato ACC Synthase: Regulation of Gene Expression and Importance of the C-Terminal Region in Enzyme Activity

Abstract

We have isolated and sequenced a tomato (Lycopersicon esculentum cv. PikRed) ACC synthase gene and expressed it in Escherichia coli. This gene encodes a wound-inducible, 1.8 kb transcript; the degree of transcript induction in red-ripe fruit was much greater than that observed in early-red fruit. Inhibitors of ethylene perception (2,5norbornadiene) or biosynthesis (salicylic acid) inhibited accumulation of the transcript, suggesting its positive regulation by ethylene. This may be a part of the molecular basis of autocatalytic ethylene production. Polyamines, which are antisenescence growth regulators, inhibited the induction of the transcript. The ACC synthase expressed in E. coli was not a fusion protein and was enzymatically active. Transformation of E. coli with an ACC synthase gene construct in which 57 amino acids from the C-terminus of the coding region were deleted, produced a truncated protein without enzymatic activity. This suggess that all or some of the C-terminal 57 amino acids are necessary for ACC synthase activity. The E. coli expression system used here seems to be valuable for investigating the structure-function relationships of this important plant protein.