Genome-wide identification and expression analysis of the 4-Coumarate: CoA ligase (4CL) gene family in melon (Cucumis melo L.)

4-Coumarate: CoA ligase (4CL) is a key branching-point enzyme in the plant phenylpropanoid metabolic pathway, playing an essential role in the synthesis of lignin, flavonoids, and other secondary metabolites. In this study, a total of 30 4CL gene family members were systematically identified for the first time, which were unevenly distributed across 10 chromosomes. Based on a maximum likelihood tree constructed exclusively using melon 4CL protein sequences, the 30 Cm4CL genes were classified into four subfamilies (I-IV), each exhibiting distinct exon-intron structures and conserved motif compositions. All Cm4CL proteins were highly conserved, containing the typical AMP-binding domain and the 4CL characteristic motif. Promoter cis -element analysis revealed that Cm4CL genes are enriched in regulatory elements associated with light response, phytohormones, and abiotic stress. Cm4CL genes displayed distinct expression differentiation; constitutively highly expressed genes such as Cm4CL24 showed high expression levels in vegetative organs and during the post-harvest stage of fruits. qRT-PCR analysis demonstrated that representative Cm4CL genes exhibited differential responses to NaCl stress and treatments with SA, ABA, and MeJA. Among them, Cm4CL1 was upregulated 4.3-fold under salt stress, and Cm4CL26 was upregulated 8.8-fold under ABA treatment. This study provides candidate genes and a foundational resource for further functional dissection of phenylpropanoid metabolism and stress tolerance breeding in melon.