Nucleotide sequence of a cDNA for 1-aminocyclopropane-1-carboxylate synthase from melon fruits.

Ethylene is a plant hormone that has an essential role in fruit ripening (Yang and Hoffman, 1984; Kende, 1993). ACC synthase (S-adenosyl-L-methionine methylethioadenosine-lyase, EC 4.4.1.14), which is encoded by a multigene family, plays a regulatory role in ethylene production. Severa1 genes for ACC synthase have been isolated from tomato (Rottmann et al., 1991), mung bean (Botella et al., 1992, 19931, winter squash (Nakajima et al., 1990; Nakagawa et al., 1991), and Arabidopsis (Liang et al., 1992; Van Der Straeten et al., 1992). Two ACC synthase genes (LE-ACS2 and LE-ACS4, which are identified as a wounding and a ripening inducing gene, respectively) are expressed during ripening of tomato fruits (Olson et al., 1991; Rottmann et al., 1991). An antisense RNA experiment with LEACS2 reduced the levels of mRNAs for LEACS2 and LEACS4 in tomato fruits and caused retardation of initiation of ripening of tomato fruits (Oeller et al., 1991). These results showed that wound-induced ACC synthase also played an important role in the production of ethylene in tomato fruit during ripening. We isolated a cDNA (pMEACS1,2097 bp) for ACC synthase from wounded mesocarp tissue of melon fruits (Cucumis melo L. cv AMS) (Table I). The polypeptide derived from the cDNA in Escherichiu coli had ACC synthase activity. Sequence analysis of this cDNA revealed the presente of an open reading frame of 493 amino acids. This polypeptide contained seven sequences that were conserved among other ACC synthases. pMEACSl showed high homology at the amino acid and nucleotide levels to wound-induced ACC synthase from squash (Nakajima et al., 1990; Sato et al., 1991). RNA blot analysis showed that the level of mRNA for the gene increased in the mesocarp tissue of melon fruits after wounding and also during ripening. Since we could detect cDNA only for MEACSl ACC synthase in a PCR experiment with the mRNA from mesocarp tissue of ripe melon fruits, MEACSl should be the gene that is preferentially expressed during ripening of