Hence, we speculated that both CmCAD2 and CmCAD5 could be involved in fruit development. While CmCAD2 only belonged to group I as bona fide CADs, and may be likely main candidate gene for lignin biosynthesis in melon. However, little information is available on the role of CAD in relation to the lignification of melon flesh tissue during fruit development and ripening. These findings implied that melon CAD genes might also be involved in the lignification of flesh tissue, and there were difference in function among family members. There were significant expression differences between Carfilzomib 868540-17-4 CmCAD4 and other CmCADs in different tissues and during development and ripening. These observed differences could partly be explained by the amino acids differences at position 58–59. CmCAD4 had a KL motif, whereas other CmCADs had an either EW or DL/EL motif. Furthermore, based on our analysis of CmCADs, CmCAD4 had little key residues, and had a Ser123 instead of Asp123 which was suggested to be involved in determining the activity of all bona fide lignifying CADs; One mutation, D123S, resulted in a essentially inactive protein. On the basis of the above results, it appears that CmCAD4 is a pseudogene. But we used the expressed sequence tag database in NCBI as a source of mRNA sequence bioinformatics for CmCAD4, and we found that CmCAD4 showed the highest homology with a Cucumis melo cDNA clone , obtained from callus, from EST database of melon. Hence, It appears that CmCAD4 is specifically expressed in callus. Further researches are needed to confirm this speculation. We also studied the effect of ABA and IAA on CmCADs expression. ABA is extensively involved in the plant’s response to abiotic stresses, such as drought, low temperature and osmotic stress, and also regulates a variety of growth and developmental processes, and can regulate the expression of relevant genes to increase plant adaptability. ABA has been shown to induce CADs genes expression in sweet potato, ginkgo and tea after exposure to biotic or abiotic stresses. Real time qPCR and semi-quantitative PCR analysis of CmCADs in response of ABA suggested that ABA treatment increased the expressions of CmCAD1, 2, 3 and 5. Purportedly, ABAmediated plant responses to drought stress may be related to the regulation of relevant genes by the MYB transcription factor. However, to the best of our information, there were no reports on effect of ABA or IAA on ripening specific CADs. Promoter analysis of the five melon CADs suggested the presence of ABA responsive ABRE motif in the promoter of CmCAD1, 2,3 and 5, and the promoter of CmCAD1 and CmCAD5 contains response elements to IAA. Therefore, the ABAinduced these CmCADs expression observed in present study may be related to the upstream MYB response elements. However this speculation has to be demonstrated by further cloning and function analyses of the promoter of CmCADs. Auxin also plays a role in fruit development and ripening.