Two genes (CM-AAT1 and CM-AAT2) with strong sequence homology (87% identity at 
the protein level) putatively involved in the formation of aroma volatile esters 
have been isolated from Charentais melon fruit. They belong to a large and 
highly divergent family of multifunctional plant acyl-transferases and show at 
most 21% identity to the only other fruit acyl-transferase characterized so far 
in strawberry. RT-PCR studies indicated that both genes were specifically 
expressed in fruit at increasing rates in the early and mid phases of ripening. 
Expression was severely reduced in ethylene-suppressed antisense ACC oxidase 
(AS) fruit and in wild-type (WT) fruit treated with the ethylene antagonist 
1-MCP. Cloning of the two genes in yeast revealed that the CM-AAT1 protein 
exhibited alcohol acyl-transferase activity while no such activity could be 
detected for CM-AAT2 despite the strong homology between the two sequences. 
CM-AAT1 was capable of producing esters from a wide range of combinations of 
alcohols and acyl-CoAs. The higher the carbon chain of aliphatic alcohols, the 
higher the activity. Branched alcohols were esterified at differential rates 
depending on the position of the methyl group and the nature of the acyl donor. 
Phenyl and benzoyl alcohols were also good substrates, but activity varied with 
the position and size of the aromatic residue. The cis/trans configuration 
influenced activity either positively (2-hexenol) or negatively (3-hexenol). 
Because ripening melons evolve the whole range of esters generated by the 
recombinant CM-AAT1 protein, we conclude that CM-AAT1 plays a major role in 
aroma volatiles formation in the melon.