Cloning and differential expression analysis of defensin geneCldef2.2from watermelon (Citrullus lanatus(Thunb.) Matsum. & Nakai)

Abstract

Plant defensins (PDFs) are small cysteine rich peptides with potential antifungal activity. In this work, a defensin-like cDNA of 237 bp was cloned from watermelon and named Cldef2.2 (GenBank accession No. KC481268). The amino acid sequence deduced from the coding region comprised 78 amino acids with a predicted molecular mass of 8.65 KD and isoelectric point of 8.325. Sequence alignment showed that Cldef2.2 had high amino acid homology to known PDF proteins from other plant species and contained the highly conserved eight cysteine motif. Phylogenetic analysis indicated that Cldef2.2 belongs to the Arabidopsis PDF2 cluster and is close to AtPDF2.5. Real-time PCR analysis revealed that Cldef2.2 was expressed in all the examined tissues, including leaves, roots, and stems. The highest expression level was observed in roots. We also investigated the differential expression profiles of Cldef2.2 gene in response to signalling molecules such as salicylic acid (SA), methyl jasmonate (MeJA) and ethylene or in response to Fusarium oxyporum f. sp. niveum (FON) challenge. For signalling molecules, Cldef2.2 was shown to be quickly induced by MeJA at 4 h after treatment (hat), while its response to ethylene and SA was relatively slow with the expression peaking at 48 hat. For FON challenge, Cldef2.2 showed highly responsive with mRNA accumulation peaking at 4 h after inoculation (hai).