Nucleotide sequence of a cDNA encoding 1-aminocyclopropane-1-carboxylate oxidase from senescing orchid petals.

Pollination of flowers induces a suite of developmental events that lead to successful production of seeds. These events may include senescence of nonessential floral organs, development of the ovary and accessory structures, and floral color changes that serve as cues to pollinators. Many of these processes are mediated through the plant hormone ethylene, which is induced following pollination in climacteric flowers. It is well established that senescence of the perianth of many flowers is induced by ethylene, and recent work by our laboratory has further demonstrated that growth of the ovary and normal development of the male gametophyte in Phalaenopsis orchids are dependent on the production of ethylene (Zhang and ONeill, 1993). For this reason, we have examined the regulation of ethylene biosynthesis following pollination in detail. Ethylene is synthesized through the conversion of Sadenosyl L-Met to ACC by the rate-limiting enzyme ACC synthase; ACC is then oxidized to ethylene by the enzyme ACC oxidase (Yang and Hoffman, 1984). The identification of a cDNA induced in ripening tomato fruit (Holdsworth et al., 1987) and subsequent proof that it encoded ACC oxidase by antisense experiments (Hamilton et al., 1990) and expression in yeast (Hamilton et al., 1991) and Xenopus oocytes (Spanu et al., 1991) has allowed the regulation of this enzyme to be explored. Previously, we reported the identification of OAOl, an ACC oxidase identified from a cDNA library constructed to mRNA transcripts from gynoecia of Doritaenopsis flowers. This cDNA was used to demonstrate that ACC oxidase is regulated at the leve1 of transcript abundance in both the stigma and petals following pollination (Nadeau et al., 1993). Here we present the sequence of a second ACC oxidase cDNA (D-AC02) , which was isolated from a library containing transcripts from the senescing perianth of Doritaenopsis orchids (Table I). D-AC02 shares 95% nucleotide sequence homology with OAOl and encodes a proTable l. Characteristics of ACC oxidase (O-ACO2) from senescent perianth