Cloning and characterization of a plant defensin VaD1 from azuki bean

A recombinant mungbean defensin VrD1 was previously shown to exhibit antifungal and bruchid-resistant activity. To study the function and regulation of VrD1, genomic DNAs of plant defensins were isolated from Vigna radiata VC6089A and azuki bean Vigna angularis Kao Hsiung No. 6. The azuki bean defensin genomic DNA VaD1 was sequenced and converted to VaD1 cDNA. VaD1 defensin was purified from Vigna angularis Kao Hsiung No. 6 to apparent homogeneity. The complete amino acid sequence of the purified VaD1 was determined and was found to be exactly the same as the sequence deduced from VaD1 cDNA. VaD1 is a basic protein containing 46 amino acids with four conserved disulfide bonds and shares high sequence homology (78.3%) with VrD1. VaD1 inhibited the growth of Fusarium oxysporum, Fusarium oxysporum f. sp. pisi, Staphylococcus epidermidis, and Salmonella typhimurium. VaD1 also inhibited in vitro protein synthesis and bruchid larval development, but was less active than the recombinant VrD1.