Psc-AFP, isolated from the seeds of Psoralea corylifolia L., is an antimicrobial protein with trypsin inhibitor activity. Its encoding gene was cloned by 3'- rapid amplification of cDNA ends (RACE) combined with Y-shaped adaptor-dependent extension (YADE) method. The gene Psc-AFP encodes a protein of 203 amino acids with a deduced signal peptide of 24 residues. The growth inhibition effect exerted by the heterologously expressed Psc-AFP in Pichia pastoris revealed that the recombinant Psc-AFP inhibited mycelium growth of Aspergillus niger, Rhizoctonia solani, and Alternaria brassicae and conidial germination of Alternaria alternata. The recombinant Psc-AFP also showed protease inhibitor activity manifested by the inhibition of trypsin. The transgenic tobacco bioassays confirmed that overexpressing Psc-AFP significantly enhanced the disease resistance of tobacco and that some of the transgenic lines were almost fully tolerant to Ralstonia solanacearum and A. alternata, whereas no apparent alteration in plant growth and development was observed. Collectively, these results indicate that the recombinant Psc-AFP is an active antimicrobial protein, with protease inhibitor activity that can be successfully produced in the yeast and tobacco and, therefore, maybe a potential antimicrobial candidate for practical use.
Keywords: Antimicrobial protein; Heterologous expression; Pichia pastoris; Psoralea corylifolia; Tobacco; Trypsin inhibitor.