Cloning and characterization of a cDNA encoding an antimicrobial protein from mung bean seeds

A cDNA clone, VrCRP (GenBank accession no. AF326687), encoding an antimicrobial protein was isolated from the differentially expressed cDNAs between a pair of near isogenic lines of mid-matured mung bean seeds. Northern blot analysis showed that VrCRP gene is preferentially expressed in bruchid-resistant developing mung bean seeds. The mature VrCRP is a basic cysteine-rich protein with a predicted molecular mass of 5.9 kDa and a calculated isoelectric point of 8.23. Eight cysteine amino acids present in the primary structure of VrCRP compose four disulfide bridges. Biological analysis showed that VrCRP is toxic to E. coli and completely arrested growth of insect cell (Spodoptera frugiperda, Sf21) at a low concentration of 3.42 μM. VrCRP also inhibited the growth of Rhizoctonia solani. Immunolocalization and in situ hybridization indicated that VrCRP was predominantly present in the parenchyma cells of the seed coat. Based on the biological activities and the protein localization, it is suggested that VrCRP may act as an evolutionary barrier in mung bean seeds that is important in coping with invasions of pathogens and herbivores.