Molecular cloning and expression analysis of two genes encoding plant defensins from watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai)

Summary

Plant defensins (PDFs) are innate anti-microbial peptides that play important roles in disease resistance, particularly resistance to fungi. Two defensin-like cDNA sequences were cloned from watermelon and named ClPDF2.4 (GenBank Accession No. KC481270) and ClPDF2.5 (GenBank Accession No. KC481271). Sequence alignments showed that the encoded proteins ClPDF2.4 and ClPDF2.5 had high amino acid sequence homology (> 62%) to known Arabidopsis PDF proteins and contained a highly conserved motif of eight cysteine residues. Phylogenetic analysis indicated that both ClPDF2.4 and ClPDF2.5 belonged to the Arabidopsis PDF2 cluster and were closely-related to each other. Real-time quantitative PCR analysis revealed that the ClPDF2.4 and ClPDF2.5 genes were expressed in a wide variety of tissues, including leaves, roots, and stems. The highest level of expression of both genes was observed in leaves. The level of transcription of ClPDF2.5 was higher than that of ClPDF2.4 in stems. Gene expression profiles in response to signalling molecules such as salicylic acid (SA), methyl jasmonate (MeJA), and ethylene, or in response to a challenge inoculation with Fusarium oxysporum f. sp. niveum (FON) were investigated. Expression levels of ClPDF2.4 and ClPDF2.5 were shown to be highly induced in response to signalling molecules, but were down-regulated when roots were infected by FON. Furthermore, expression of the ClPDF2.4 and ClPDF2.5 genes was differentially induced in response to different stimuli.