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 pepti de, the gene for sarcotoxin IA, which is an antimicrobial peptide from an insect consisting of 39 amino acid residues, was introduced into t obacco (Nicotiana tabacum) under the control of a high expression prom oter via Agrobacterium-mediated transformation. In transgenic plants, sarcotoxin IA mRNA accumulated to detectable levels, however, the amou nt of the peptide produced was so small that we could scarcely detect it by protein gel blot analysis, probably because of the instability o f short peptides in plant cells. To improve the expression efficiency, genes for four types of amino-terminal and carboxyl-terminal translat ional fusions of sarcotoxin IA together with the GUS gene were introdu ced 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-sar cotoxin IA and GUS antibodies showed production of high levels of fusi on protein in all transgenic plants. Among therm, three types had abno rmal membranes and phenotypes, although no such abnormalities were fou nd in transgenic plants in which only sarcotoxin IA was expressed in a secretable form. All together, these results indicated that, for stab le and effective expression of a foreign short peptide in transgenic p lants, expression as a fusion protein is useful and that secretion of sarcotoxin IA outside of cells is necessary for generation of useful a ntimicrobial transgenic plants.