Antibacterial and Antifungal Activity of a Snakin-Defensin Hybrid Protein Expressed in Tobacco and Potato Plants

To enhance plant protection against phytopathogens, we constructed a fusion gene (SAP) for the simultaneous production of snakin-1 (SN1) and defensin-1 (PTH1) cysteine-rich antimicrobial proteins originally identified in potato. Prior to in vivo evaluation of antimicrobial activity, SAP produced in Escherichia coli was tested in in vitro against four phytopathogenic microorganisms. SAP exhibited the highest antimicrobial activity against the bacterium Clavibacter michiganensis subsp. sepedonicus, which is the cause of potato ring rot disease, and the anthracnose-causing fungus Colletotrichum coccoides, by complete inhibition of cell growth or spore germination, respectively, at a concentration of 6 M. Notably, SAP showed higher inhibitory activities against Pseudomonas syringae pv. syringae, P. syringae pv. tabaci and Colletotrichum coccoides, than individual SN1 and PTH1, whereas its effect on C. michiganensis subsp. Sepedonicus in in vitro was comparable to that of PTH1 alone. Antimicrobial activity of SAP against C. coccoides and C. michiganensis subsp. sepedonicus was assessed in plants on Nicotiana benthamiana and Solanum tuberosum, respectively, using SAP expressed from the Potato virus X-based vectors pP2C2S and/or pGR107. Both SAP-producing plants were significantly more resistant to infection than control plants. Our results demonstrated that in vivo coproduction of recombinant SN1 and PTH1 as a hybrid protein is a promising strategy for antimicrobial plant defense