RESUMEN
Biotin-binding proteins (BBPs), expressed in transgenic plants, are insecticidal to a very wide range of insects. The expression levels required are generally low (approximately 100 ppm), and although higher than required for Bacillus thuringiensis (Bt) delta-endotoxins, BBPs are effective across a broader range of insect orders and other invertebrates than the Bt Cry proteins. Avidin and streptavidin, in particular, have been reported as causing death or severe growth reduction in at least 40 species of insects across five insect orders (Lepidoptera, Coleoptera, Orthoptera, Diptera, and leaf-eating Hymenoptera) and mites. In addition, due largely to its rapid dilution in ecosystems, no adverse impacts on nontarget microorganisms or invertebrates have been recorded. Because the target, biotin, cannot itself be modified to prevent it binding to BBPs and remain effective as a vitamin, the major avenue open to insects to develop resistance is unavailable. Two properties of the biotin-avidin complex make it highly suitable for use in transgenic plant crop protection strategies against a large range of insects; its extreme stability and its resistance to proteolysis. However, because the nutritional value of the plant could potentially be compromised in the absence of biotin supplementation, its use in nonfood crops such as fiber, forestry, and biofuel crops is seen as the most suitable initial focus for this technology.