The limited value of measuring gene flow via errant pollen from GM plants

Abstract

Since the advent over 30 years ago of recombinant DNA technologies giving rise to genetically engineered organisms (often called GMOs), gene escape from such transgenic organisms has been a consistent and legitimate concern. Initially, the fear of GM microbes escaping and wreaking ecological havoc on the biosphere generated both well funded scientific analyses of the actual threat, and fueled science fiction tracts of rampant monster microbes consuming every living thing on Earth. In recent years the focus—at least in the scientific community—has shifted to GM plants, particularly the incidence of escape of genes from GM crops. The lion’s share of the funding and research effort has gone to study gene escape via pollen dispersal. Each species has different pollen flow characteristics, from the vectors, to the distance, to the list of prospective recipient species and varieties. Some crops, like maize/corn and Brassica napus, produce large amounts of viable pollen and outcross notoriously; such species spawn plenty of research attention from both scientists and granting agencies. As a result, this journal and other literature is now teeming with data, models and evidence documenting the likelihood, mechanisms and incidence of pollenmediated gene flow from transgenic plants. Most crop plants produce pollen, and pollen can be carried by wind, insects, animals or other vectors to distant locales where they may successfully pollinate a waiting recipient. The recipient could be another plant of the same species, but a different (GM or non-GM) cultivar, or it could be a compatible relative, with or without weedy characteristics. Depending on the nature of the gene and the recipient, the resulting hybrid may or may not cause concern. In the most benign situation, for example, a pollen grain from a GM or non-GM plant might blow or be carried across the road to pollinate another plant of the same cultivar growing in a neighbor’s field. Although this is clearly an example of gene escape and outcrossing, few scientists would get excited (let alone funded) to investigate and measure the incidence or implications of such events. Indeed, how would one even detect this eventuality, given the background of genetically identical proximal sources of pollen? How would one distinguish the pollination from an adjacent plant as opposed to the pollen grain of a genetically identical plant from across the road? At the other end of the spectrum, we can envisage a situation in which gene escape is important, for example in plants engineered to produce pharmaceutical or potentially toxic industrial compounds. Similarly, genes conferring ecological fitness traits such as drought or salt tolerance would be problematic if the genes were to escape cultivation and wind up in plants out-competing other plants in unmanaged ecosystems. The main ecological hazard here is genetic proliferation and spread beyond intended borders. Increased ecological fitness is a real hazard and warrants considerable research. But not all GM genes confer fitness traits, and many fitness (or ‘weedy’) characteristics appear in non-GM plants. The point of these investigations is to inform the scientific community, regulators and society at large of the relative hazards posed by GM crops. But the pollen flow studies, although necessary, are insufficient because (1) measures of pollen flow don’t identify actual hazards (if any) posed as a consequence of the inevitable gene escape and (2) without some comparative data we don’t whether pollen-based gene flow is a greater or lesser means of gene escape than other common routes (such as seed spillage or volunteerism). Unless and until we compare pollen-based gene flow with other means of gene escape, we cannot properly inform policymakers, and thus we are incomplete in our scientific assessments.