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

Abstract

A cDNA corresponding to plastidic glutamine synthetase (GS-2), an enzyme involved in photorespiration, was expressed in antisense orientation under the control of a leaf-specific soybean ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit gene promotor in transgenic tobacco to yield conditionally lethal plants. Three transgenic tobacco lines with decreased (at most 64%) foliar GS-2 activity were obtained. These plants grew normally when maintained in an atmosphere with a CO 2 partial pressure sufficiently high (300 Pa CO 2) to suppress photorespiration. However, when photorespiration was initiated by the transfer of the plants to air (35 Pa CO 2), ammonium accumulated in the leaves. With time, the transgenic plants exhibited severe chlorotic lesions and, eventually, the plants died. A stable atmosphere containing at least 300 Pa CO 2 can be established easily in the greenhouse but is unlikely to occur in a natural environment. Therefore, the transgenic tobacco plants with decreased leaf GS-2 activity may contribute to biological safety for production of desired proteins.