Environmentally Friendly Approaches in Biotechnology: Engineering the Chloroplast Genome to Confer Stress Tolerance

摘要

Chloroplast genetic engineering is emerging as an alternative new technology to overcome some of the potential environmental concerns of nuclear genetic engineering (reviewed in ref 1). One commonly perceived environmental concern is the escape of foreign gene through pollen or seed dispersal from transgenic crop plants to their weedly relatives creating super weeds or causing genetic pollution among other crops (2). High rates of such gene flow from crops to wild relatives (as high as 38% in sunflower and 50% for strawberries) are certainty a serious concern. Keeler et al. (3) have summarized valuable data on the weedy wild relatives of sixty important crop plants and potential hybridization between crops and wild relatives. Among sixty crops, only eleven do not have congeners (members of the same genus) and the rest of the crops have wild relatives somewhere in the world. In addition, genetic pollution among crops has resulted in several lawsuits and shrunk the European market for organic produce from Canada from 83 tons in 1994-1995 to 20 tons in 1997-1998 (4). For example, a canola farmer in Canada cultivated a glyphosate (Round-up( resistant cultivar (Quest) and a glufosinate (Liberty)-resistant cultivar (Innovator) 30 meters away across an intervening road that exceeds the standard buffer zone of 6 meters. Two applications of Round-up herbidice in 1998 to the field sown with glufosinate resistant cultivar killed all the weeds but revealed glyphosate resistant cultivar killed all the weeds but revealed glyphosate resistant canola in the field sown with other cultivars. This population was thickest near the road, where airborne dispersal of pollen from glyphosate resistant canola could occur. Meanwhile, a Canadian farmer is being sued by Monsanto for possessing and growing glyphosate resistant canola without a license, however, the farmer claims that his crops were contaminated by resistant genes via wind or bee pollination. Because of all these concerns, Canadian National Farmers Union is lobbying the Canadian Federal GOvernment to legislate industry compensation for unintended genetic alteration of crops (4). Several major food corporations, including ADM have required segregation of native crops from those polluted with transgenes. Two legislations have been submitted in the U.S. to protect organic farmers whose crops inadvertently contain transgenes via pollen drift (5). Maternal inheritance of foreign genes through chloroplast genetic engineering is highly desirable in such instances where there is potential for out-cross among crops or between crops and weeds (6-8).