Genes outside of context

July 2016
Photo Creative Commons
A review article by the Rothamsted Research team developing GM plants with fish oil [1] describes the scientific process by which their novel crop was created.

'Omega-3' fish oils are essential dietary requirements for fish and humans. Their sole source in the food chain is tiny, one-cell organisms such as algae and some bacteria which are eaten by fish which are, in turn, eaten by humans. Fish-farming is now wide-spread and provides an effective system for producing animal protein for human consumption. Currently, farmed fish are fed on wild fish stocks and omega-3 oil supplemented feed. The limited supplies of both create a bottleneck in aquaculture production and expansion, and are environmentally damaging. GM fish-oil producing crops offer a promising and more sustainable alternative.

The Rothamsted review describes how it identified the various metabolic pathways by which different marine microbes synthesize omega-3 oil. These provided a toolkit of genes and the enzymes they encode which the scientists could copy into oilseed plants.

Creation of omega-3 by a living cell is a multistep process, requiring numerous genes to generate the enzymes needed for each stage. Manufacturing the genes and associated regulatory DNA to achieve a plant which successfully produces and accumulates fish oil is, of course, fraught with difficulties.

These difficulties, as outline by the Rothamsted scientists, illustrate very well why GM plants could be, or become, unsafe to eat.

First, an artificial gene construct (or edited gene) will impose a novel biochemical process on the metabolic context of the modified plants. Enzymes act on a substrate which is also a vital part of the metabolic context. An artificial enzyme will alter all the natural biochemical processes linked to that substrate. This disruption is likely to weaken the plant, but may not be noticed until environmental stresses in the field add to the problem.

Secondly, the plant will try to resist the novel process imposed on it, trapping or diverting intermediate products down other biochemical pathways with possibly toxic results. Measurements of the desired end-products, such as enzymes or oils, may not identify these.

Thirdly, complex synthesis requires the co-ordinated expression of all the artificial genes. Natural gene-systems are co-ordinated by the whole cell. Artificial gene-systems are, at best, co-ordinated by some part of the whole or, at worst, co-ordinated only by themselves. This spells disruption to plant health and to food quality, especially under stress.

The outcome is unpredictable expression of the artificial genes and their associated regulatory DNA, and unpredictable changes in the metabolism of the cell and the whole organism. This is the reason any GM trait more complex than a single Bt protein or a single enzyme to confer herbicide-tolerance just doesn't deliver [2].

OUR COMMENT

In nature, only tiny single-celled organisms, such as algae, synthesize omega-3 fatty acids. Anything bigger has to be part of a food-chain which feeds on algae at its base to get their omega-3s. The Rothamsted authors explain this away by postulating that higher animals simply don't need to make omega-3s because there are plenty in their surroundings. This blanket explanation for an apparent defect in the entire animal kingdom is less than convincing.

We can't help noticing that some omega-3s are the precursors for highly bio-active substances, and that there’s evidence some can be toxic to wildlife at high concentrations in an unnatural diet [1]. Perhaps limiting their presence to the food chain where animals are naturally selective about what they eat is a safer option for maintaining a diverse, balanced and stable ecosystem.

Background:

[1] GM-FED BUTTERFLIES DON'T FLY - July 2016

[2] SIMPLY, FUSSY PLANTS - July 2016

SOURCE

  • Jonathan A. Napier, et al., 2015, Transgenic plants as a sustainable, terrestrial source of fish oils, European Journal of Lipid Science and Technology, 117

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