In this work,a defensin-like cDNA sequence was cloned from watermelon,named ClPDF2.1 (GenBank accession No.KC481267).Bioinformatics analysis showed that ClPDF2.1 encodes a putative polypeptide of 75 amino acids with a calculated molecular mass of 8.237 kD and a theoretical pI of 9.375.Sequence alignment showed that ClPDF2.1 had high homology to known PDF proteins from other plant species and contained the conserved eight cysteines motif.Phylogenetic analysis indicated that ClPDF2.1 belonged to the Arabidopsis PDF2 cluster,and was close to Capsicum annuum PDF gene with an overall sequence identity of 59%.Real-time PCR analysis revealed that ClPDF2.1 expressed in all tissues examined,with the highest in leaves,second in roots and the lowest in stems.Expression profiles under different treatments such as abscisic acid (SA),methyl jasmonate (JA),ethephon (ETH) and Fusarium wilt were compared,and the results revealed that transcriptional level of ClPDF2.1 was obviously up-regulated.These results suggested that ClPDF2.1 is probably employed the signal pathways to defense against Fusarium wilt pathogen.