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Posted: December 2014

Potential Unintended Effects of RNAi-based Insecticidal Crops

A new form of genetic engineering is being developed in which genetically modified plants make a special kind of RNA that, when taken up by insect pests, can induce harmful effects through silencing genes in the insect. Two USDA scientists have written a review article discussing the manifold potential unintended effects of this technology, especially in connection with harming nontarget insects.

This new technique is called RNA interference (RNAi). The idea is to genetically modify crop plants to produce a specific type of double-stranded RNA (dsRNA), which is then taken up by insects that feed on the plant. This dsRNA is subsequently broken down into small interfering RNA strands (siRNA) that, in a complex process, silence the activity of a specific gene in the pest, which in turns weakens or even kills the pest. The technique has been tested experimentally and shown to work in principle (with varying degrees of actual harm to the pest).

USDA research entomologists Jonathan Lundgren and Jian Duan (2013) discuss a number of different unintended effects that the widespread planting of RNAi genetically modified crops could have. Their focus is on potential effects on nontarget organisms that would ingest the GM crops, including human beings.

Here are some of their concerns about unintended effects of small interfering RNAs (siRNA). In the article they provide examples out of the scientific literature to underscore these concerns.
  • siRNAs may silence the target gene in nontarget insects (or other organisms) and thereby harm or kill them.
  • Although siRNAs are purported to target specific genes to silence, the literature shows that they commonly silence unintended genes in the target organisms, which can lead to undesired effects in the target organism.
  • Similarly, siRNAs could silence unintended genes in nontarget organisms.
  • siRNAs have been found to stimulate immune reactions in mammals. “It is unclear how the immune systems of other organisms will react to an influx of small RNAs. Nor is it known how this immuno-stimulation will affect the fitness of nontarget organisms.”
  • Foreign siRNAs may saturate a cell’s RNA interference system and thereby negatively impact the ability of cells to regulate their own gene expression.
  • Many nontarget species will be exposed to the RNA-based GM crops. “Knowledge gaps make it unclear how dsRNAs that target a pest will function with the RNAi pathways of other organisms (especially phylogenetically divergent ones).”
  • Since both the physiological state of an organism and the specific environmental conditions play a large role in when genes are expressed and how genes are expressed in a given time and place, it will be very difficult to predict nontarget effects based on laboratory experiments or even small field experiments.
Lungren and Duan point repeatedly to “knowledge gaps” in assessing the broader impacts of this technology. It seems evident that applying great caution in allowing commercialization of RNA-based GM crops is warranted.

Lundgren, J. G. and J. J. Duan (2013). “RNAi-Based Insecticidal Crops: Potential Effects on Nontarget Insects,” BioScience vol. 63, pp. 657-65. doi: 10.1525/bio.2013.63.8.8

Note: The authors are research entomologists with the U.S. Department of Agricultural Research Service in Washington, D.C.

Copyright 2014 The Nature Institute.

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