This invention provides: 1) methods for the identification of broad-spectrum holins with a high level of nonenzymatic activity in membranes; 2) conditions required for maintaining and increasing the anti-microbial and anti-pest efficacy of holins in gene fusions; 3) a method for effective targeting of holins expressed in plants through use of a leader peptide to direct the holin protein to the plant apoplast and xylem; 4) methods for the control of bacterial and fungal diseases of plants and control of insect and nematode pests that attack plants by expression of gene fusions involving holins, C-terminal additions and leader peptides, and optionally, endolysins; 5) methods for increasing the shelf-life of cut flowers, and 6) transgenic plants useful for the production of novel antimicrobial proteins based upon holins.