Efforts toward engineering resistance against Tobacco etch virus by expressed peptide inhibitors and broad-spectrum resistance by expressed protein elicitors of defense

Members of a random peptide library were selected as inhibitors of the Tobacco etch virus (TEV) protease in a bacterial in vivo selection system. They were expressed in tobacco and evaluated for the ability to protect plants from TEV infection. Some inhibitors proved effective in providing enhanced TEV resistance when compared to non-transgenic plants. Therefore, it is likely that this approach may be used to engineer specific resistance against other potyviruses by targeting their proteases.;As a method of providing broad-spectrum resistance against a variety of pathogens, an elicitin, parasiticein from Phytophthora parasitica , was transiently expressed in tobacco under different targeting conditions. Elicitins trigger a rapid localized cell death called the hypersensitive response (HR) in tobacco leaves and a systemic acquired resistance (SAR) against subsequent pathogen attack. The effect of signal peptide (SP) and endoplasmic reticulum (ER) targeting sequences on the HR-inducing ability of elicitin genes were examined by transient and stable expression. Results reveal that SP targeting sequences are required for HR induction by parasiticein under the expression conditions used. Furthermore elicitin expression in vivo requires very tight regulatory control to avoid damage by low level expression in plants. Even seedlings are elicitin responsive. Germination of tobacco seedlings exposed to 1 muM elicitin was inhibited. These findings should add to efforts employing elicitins to engineer defense responses in tobacco and other plants.