Cloning of genes differentially expressed during the initial stage of fruit development in melon (Cucumis melo cv. Reticulatus)

We have cloned genes involved in the initial stage of fruit development in the melon by suppression subtractive hybridization. A cDNA library of unfertilized ovules was subtracted from that of fruit 9 days after pollination (DAP); 10 of the 40 selected cDNA clones were identified by reverse Northern analysis as genes differentially expressed in fruit at 9 DAP. Seven of the ten genes were homologous to genes of known function; two were related to genes with unknown functions, and one was novel. With the exception of cucumisin, none of the cDNAs had been previously identified in melon. According to Northern analyses, six of the genes were expressed at high levels early in fruit development. Expression of cucumisin, Cmf-25, Cmf-30, and Cmf-124 was highest at 9 DAP, implying that these genes are involved in the initial stage of fruit development. Cmf-30, a seed nucellus-specific gene, was also expressed early in seed development. The other genes were expressed at a moderate level throughout fruit development, with the highest expression occurring in fruit at 9 and 18 DAP. In conclusion, nine new genes involved in early fruit development in melon were cloned, and their temporal and spatial expression patterns indicate that they are preferentially expressed during the active growing stage of fruit.