Nucleotide Sequence of the Nicotiana tabacum cv Xanthi Gene Encoding 1-Aminocyclopropane-1-Carboxylate Synthase.

Ethylene is a plant hormone that influences many aspects of plant growth and development (10). The biosynthetic pathway of ethylene production in higher plants is well defined. The rate-limiting step in this pathway is the reaction catalyzed by ACC' synthase (S-adenosyl-L-methionine methyl-thioadenosine-lyase, EC 4.4.1.4), which converts Sadenosyl-L-methionine to ACC. Tobacco (Nicotiana tabacum) has been used extensively to study the importance of ethylene in plant defense responses. It has been known for some time that ACC synthase activity is enhanced in tobacco leaves undergoing a hypersensitive response to pathogen attack (3). An EIX produced by the fungus Trichoderma viride elicits ethylene biosynthesis in N. tabacum cv Xanthi leaf tissue (2). When EIX is applied to the petiole of a detached tobacco leaf, it moves throughout the leaf and, consequently, induces ethylene production and tissue necrosis (1). If the tobacco leaves are first incubated with ethylene, the response to EIX treatment is greatly enhanced. mRNA was prepared from N. tabacum cv Xanthi leaves preincubated with ethylene and then challenged with EIX to induce copious ethylene biosynthesis. We amplified from the above tobacco mRNA an ACC synthase gene fragment (450 bp) using the polymerase chain reaction and two degenerate primers based on the noncoding strand of the tomato ACC synthase gene (9). We used this fragment to isolate a cDNA clone (pTACC-13) of an ACC synthase gene. This clone was isolated from a cDNA library prepared from N. tabacum cv Xanthi leaves treated as stated above. The clone, pACC-13, was then introduced into Escherichia coli (XL1-Blue, Stratagene2), and accumulation of low levels of ACC was observed (data not shown), indicating expression of a functional ACC synthase gene (5). We report here the ACC synthase gene sequence of N. tabacum cv Xanthi (Table I, Fig. 1). The sequence includes the 1473-bp coding region of the N. tabacum gene and 153 bp