ISOLATION OF A RIPENING AND WOUND-INDUCED CDNA FROM CUCUMIS-MELO L ENCODING A PROTEIN WITH HOMOLOGY TO THE ETHYLENE-FORMING ENZYME

A cDNA clone (pMEL1) was isolated from a climacteric melon fruit cDNA library using the tomato ethylene-forming-enzyme (EFE) cDNA, pTOM13, as a probe. Northern analysis of RNA isolated from wounded leaf and fruit tissue and from preclimacteric and climacteric pericarp tissue was used to determine the pattern of pMEL1 RNA expression. pMEL1 hybridized to a 1.3-kb transcript in climacteric fruit and wounded leaf tissue but was undetectable in preclimacteric fruit and unwounded leaves. Maximal expression of pMEL1 RNA occurred in wounded ripe fruit. pMEL1 contained a 1230-bp insert containing a predicted open reading frame of 318 amino acids and molecular mass of 35.3 kDa. The predicted amino acid sequence of pMEL1 was 73 - 81 % identical to the deduced amino acid sequences of tomato (pTOM13) EFE and EFE-related genes isolated from tomato and avocado fruit and senescent carnation petals. Genomic Southern analysis indicated that pMEL1 hybridized to a number of genomic fragments consistent with the presence of more than one pMEL1-related gene in melon. On Western analysis of total protein extracts from ripe tomato and melon fruit, using an antibody raised against tomato EFE (pTOM13) expressed in Escherichia coli, a single 35.5-kDa protein was detected. A 35-kDa product translated from in-vitro transcribed pMEL1 and immunoadsorbed by anti-EFE serum was very similar in size to the predicted 35.3-kDa pMEL1 cDNA protein product. These results indicate that pMEL1 may encode an EFE gene involved in ethylene biosynthesis during fruit ripening and may be identical to or share extensive sequence similarity with an EFE expressed in response to tissue wounding.