Greenhouse-grown conditionally lethal tobacco plants obtained by expression of plastidic glutamine synthetase antisense RNA may contribute to biological safety

A cDNA corresponding to plastidic glutamine synthetase (GS-2), an enzyme in volved in photorespiration, was expressed in antisense orientation under th e control of a leaf-specific soybean ribulose-1,5-bisphosphate carboxylase/ oxygenase small subunit gene promotor in transgenic tobacco to yield condit ionally lethal plants. Three transgenic tobacco lines with decreased (at mo st 64%) Foliar GS-2 activity were obtained. These plants grew normally when maintained in an atmosphere with a CO2 partial pressure sufficiently high (300 Pa CO2) to suppress photorespiration. However, when photorespiration w as initiated by the transfer of the plants to air (35 Pa CO2), ammonium acc umulated in the leaves. With time, the transgenic plants exhibited severe c hlorotic lesions and, eventually, the plants died. A stable atmosphere cont aining at least 300 Pa CO2 can be established easily in the greenhouse but is unlikely to occur in a natural environment. Therefore, the transgenic to bacco plants with decreased leaf GS-2 activity may contribute to biological safety for production of desired proteins. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.