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Antimicrobial peptides (AMPs) are known to play important roles in the innate host defense mechanisms of most living organisms.Protease inhibitors from plants potently inhibit the growth of a variety of pathogenic bacteria and fungi.Therefore,there are excellent candidates for the development of novel antimicrobial agents.In this study,an antimicrobial peptide derived from tartary buckwheat seeds (FtAMP) was obtained by gene cloning,expression and purification,which exhibited inhibitory activity toward trypsin.Furthermore,the relationship between the antimicrobial and inhibitory activities of FtAMP was investigated.Two mutants (FtAMP-R21A and FtAMP-R21F) were generated through site-directed mutagenesis.Inhibitory activity analysis showed that both FtAMP-R21A and FtAMP-R21F lost trypsin-inhibitory activity.However,FtAMP-R21A and FtAMP-R21F showed novel inhibitory activities against elastase and α-chymotrypsin,respectively,suggesting that Arg-21 in the inhibitory site loop is specific for the inhibitory activity of FtAMP against trypsin.Antimicrobial assays showed that all three peptides exhibited strong antifungal activity against Trichoderma koningii,Rhizopus sp.,and Fusarium oxysporum.These results showed that the changes in FtAMP inhibitory site have no effect on their antifungal properties.