Abstract:Persea americana var. dryifolia defensin （PaDef） has a broad-spectrum antibacterial action， and it was extracted from the fruit of Mexican avocado. The structure-activity relationship and antibacterial mechanism of PaDef have not yet been clarified. Therefore， targeted molecular modification of recombination PaDef（rPaDef） was carried out by site directed mutagenesis. Finally， modified peptides rPaDefQ33H and rPaDefK43M with 2-3 fold increased antibacterial activity were obtained while maintaining good stability and low hemolysis and cytotoxicity. Scanning electron microscopy and fluorescence microscopy were used to investigate the antibacterial mechanism of rPaDef and modified peptides， indicating that rPaDef and modified peptides could create pores on the surface of bacteria， disrupt the cell integrity of the tested bacteria， and ultimately lead to bacterial death. Therefore， rPaDef and modified peptides could be used as substitutes for new antibiotics and had great application prospects in food storage and preservation， green feed additives， and clinical medicine fields.