Enhanced expression of an antimicrobial peptide sarcotoxin IA by GUS fusion in transgenic tobacco plants

To enhance the disease resistance of plants expressing a foreign peptide, the gene for sarcotoxin IA, which is an antimicrobial peptide from an insect consisting of 39 amino acid residues, was introduced into tobacco (Nicotiana tabacum) under the control of a high expression promoter via Agrobacterium-mediated transformation. In transgenic plants, sarcotoxin IA mRNA accumulated to detectable levels, however, the amount of the peptide produced was so small that we could scarcely detect it by protein gel blot analysis, probably because of the instability of short peptides in plant cells. To improve the expression efficiency, genes for four types of amino-terminal and carboxyl-terminal translational fusions of sarcotoxin IA together with the GUS gene were introduced into tobacco. In all four types of transgenic tobacco plants, high level transcripts similar to that in the direct expression sarcotoxin IA construct were Pound. Protein gel blot analysis with both anti-sarcotoxin IA and GUS antibodies showed production of high levels of fusion protein in all transgenic plants. Among therm, three types had abnormal membranes and phenotypes, although no such abnormalities were found in transgenic plants in which only sarcotoxin IA was expressed in a secretable form. All together, these results indicated that, for stable and effective expression of a foreign short peptide in transgenic plants, expression as a fusion protein is useful and that secretion of sarcotoxin IA outside of cells is necessary for generation of useful antimicrobial transgenic plants.