Characterization of a stamen-specific cDNA encoding a novel plant defensin in Chinese cabbage

We isolated a stamen-specific cDNA, BSD1 (Brassica stamen specific plant defensin 1) that encodes a novel plant defensin peptide in Chinese cabbage (Brassica campestris L. ssp. pekinensis). Plant defensins are antimicrobial peptides containing eight highly conserved cysteine residues linked by disulfide bridges. In BSD1, the eight cysteine residues and a glutamate residue at position 29 are conserved whereas other amino acid residues of the plant defensins consensus sequence are substituted. BSD1 transcripts accumulate specifically in the stamen of developing flowers and its level drops as the flowers mature. The recombinant BSD1 produced in Escherichia coli showed antifungal activity against several phytopathogenic fungi. Furthermore, constitutive over-expression of the BSD1 gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter conferred enhanced tolerance against the Phytophthora parasitica in the transgenic tobacco plants.