A cDNA Sequence from Kiwifruit Homologous to 1-Aminocyclopropane-1-Carboxylic Acid Oxidase

The plant growth regulator ethylene controls the onset of ripening in climacteric fruit (Schuch et al., 1989). Two enzymes are responsible for ethylene biosynthesis from its precursor S-adenosyl methionine: ACC synthase and ACC oxidase (Yang and Hoffman, 1984). Two cDNA clones, pTOM13 and pHTOM5, have been isolated from tomato and shown to encode ACC oxidase by expression in yeast (Hamilton et al., 1991) and Xenopus laevis oocytes, respectively (Spanu et al., 1991). In addition, expression of antisense pTOM13 RNA has been shown to inhibit ethylene synthesis by tomato fruit and wounded leaves (Hamilton et al., 1990). Severa1 fruit ripening-related genes homologous to pTOM13 have now been isolated from other species, including apple (Dong et al., 1992; Ross et al., 1992) and avocado (McGarvey et al., 1990). We report the sequence of a cDNA clone (pKIWIAO1, , Table I) isolated from a library constructed from mRNA of ripe kiwifruit (Act inidia deliciosa var deliciosa cv Hayward). The cDNA is 1245 bp long and contains an open reading frame encoding a protein of 319 amino acids. The predicted amino acid sequence shows high homology to ACC oxidase from tomato and to related genes from apple (Dong et al., 1992; Ross et al., 1992), avocado (McGarvey et al., 1990), and carnation (Wang and Woodson, 1991). Fruit of Hayward, the only widely grown cultivar of kiwifruit, are tolerant of extended periods of cold storage (6-8 months at O f 0.5OC) (Ferguson, 1984). We are studying kiwifruit ripening in an attempt to explain why Hayward has storage properties superior to other Actinidia species. Information on the expression of genes involved in ethylene biosynthesis may allow