Abstract
Potential environmental impact caused by pollen-mediated transgene flow from commercially cultivated genetically engineered (GE) crops to their non-GE crop counterparts and to their wild and weedy relatives has aroused tremendous biosafety concerns worldwide. This chapter provides information on the concept and classification of gene flow, the framework of the environmental biosafety assessment caused by pollen-mediated gene flow, and relevant case studies about transgene flow and its environmental impact. In general, gene flow refers to the movement of genes or genetic materials from a plant population to other populations. Crop-to- crop transgene flow at a considerable frequency may result in transgene 'contamination' of non-GE crops, causing potential food/feed biosafety problems and regional or international trade disputes. Crop-to- wild/weedy transgene flow may bring about environmental impacts, such as creating more invasive weeds, threatening local populations of wild relative species, or affecting genetic diversity of wild relatives, if the incorporated transgene can normally express in the recipient wild/weedy plants and significantly alter the fitness of the wild/weedy plants and populations. It is therefore necessary to establish a proper protocol to assess the potential environmental impacts caused by transgene flow. Three steps are important for assessing potential environment impacts of transgene flow to wild/weedy relatives: (i) to accurately measure the frequencies of transgene flow: (ii) to determine the expression level of a transgene incorporated in wild/weedy populations; and (iii) to estimate the fitness effect (benefit or cost) conferred by expression of a transgene in wild/weedy populations. The recently reported case of non-random allele transmission into GE and non-GE hybrid lineages or experimental populations challenges the traditional method of estimating the fitness effect for the assessment of environmental impacts of transgene flow. Furthermore, case studies of transgenic mitigation (TM) strategies illustrate ways that may reduce the impacts of a transgene on wild/weedy populations if crop-to- wild/weedy transgene flow is not preventable, such as in the case of gene flow from crop rice to its co-occurring weedy rice.