Our CRISPR food future

March 2019

DuPont Pioneer scientists published a paper in 2017 which gives an insight into where the biotech crop market is planning to go next. This study demonstrated the "utility" of the CRISPR-Cas9 system [1] in editing maize DNA for breeding drought-tolerant crops.

The study focused on a 'key' gene which controls stress tolerance in maize by altering the plant's sensitivity to the plant hormone, ethylene. When this gene is active, the cells of the plant get bigger and multiply more. Under stress, however, plants tend to conserve their resources, the gene is switched off, and growth is reduced. By adding an artificial 'on-switch', promoter 'ARGOS8', the gene can be rendered uncontrollably over-active, thus overcoming the plant's natural reaction and increasing the yield despite the adverse environmental conditions. Enter the CRISPR-Cas9 trick to insert an artificial version of the ARGOS8 promoter DNA.

In small (4m2) plot field trials, the CRISPR-edited maize had a 34% yield loss after exposure to drought conditions during flowering compared with 36% yield loss in the comparator crop. This 2% less loss scaled up to five bushels per acre (if you ignore the evidence that the comparator maize seems to have been a lower yielding one to start with, even under optimal growing conditions).

US crop breeders, including Pioneer*, have a long history of steadily improving maize drought tolerance, and there's awareness that this has come about through changes in multiple genes which, individually, have small effects.

Our future would seem to hold a succession of CRISPR edits in single native genes to further increase maize drought tolerance, achieving a loss of yield loss of a couple of percent each time.

Dr Doug Gurian-Sherman (see below) points out that the gene controlled by ARGOS8 is also important for disease resistance and fruit ripening. He also highlights that the industry mind-set which demands crop uniformity and global commodities fails to consider the real alternatives. For example, the US Rodale Institute has found that, in maize and soya, organic systems yield up to 40% more than conventional ones in times of drought, and that organic yields are competitive with conventional ones after the full transition period. Also, the current dependence on a small number of crops with low, natural drought tolerance ignores the many grain crops, such as the sorghums and millets, which have much better natural levels of drought and heat tolerance.

Doug Gurian -Sherman is a plant pathologist, previously a scientist at the US Environmental Agency (EPA) responsible for assessing human health and environmental risks from engineered plants and micro-organisms and developing biotechnology policy. He has also been on advisory bodies to the US Food and Drug Administration and National Research Council. He is currently a research consultant with 'Strategic Expansion and Trainings' focused on supporting ecologically based sustainable agriculture, food sovereignty and food equity.

OUR COMMENT

Interfering with fruit ripening and disease resistance could instil catastrophic weaknesses in the plants, even while increased resistance to certain stresses is present.

The CRISPR-derived ARGOS8 variant maize appears, at face value, to contain a single precisely located extra or swapped gene promoter. However, looking at the method used to create it suggests it could be chock full of genetic or epigenetic scars and altered gene function.

Epigenetic refers to biochemical changes which alter DNA function, but not its structure. Such DNA-associated biochemicals are vital for normal, healthy functioning of the cell, but can be subject disruptive 'epimutation' which can be far from healthy. Epigenetic changes are heritable.

Firstly, the DNA editing was carried out using particle bombardment, a technique which shoots metal particles coated with the CRISPR construct randomly into the genome of huge numbers of cells until one cell comes out 'right', and a plant can be successfully generated from it. This method is notorious for inflicting co-lateral damage in the wider genome.

Secondly, presumably because the maize tissue is tricky to regenerate into a plant, it was also genetically transformed with two genes to assist correct shoot and ovule development, plus one selectable marker gene. Interestingly, all these artificial genes, the CRISPR and other bacterial DNA needed to generate the construct are referred to as "reagents (helper genes)".

The final product is not considered a GMO because all these "reagents" are subsequently eliminated by cross-breeding the transformed plants with non-transformed ones. However, many genetic, epigenetic and functional molecular scars could be retained in these 'non-GM' sons-of-a-GMO.

Due to the extent of its unorthodox 'ancestry', it's impossible to define a true 'control' plant with which to compare these DNA-engineered organisms. This is also the case in a less complex way for any hybrid crop. However, in the more rational, pre-GM, past of 1991, Pioneer defined a bench-mark variety of its maize as a reference to which all other hybrids could be compared. This doesn't suit the modern biotech industry, which likes to cherry-pick its comparators to prove its point.

Tell your regulators not to be conned by biotech industry claims of how minor and precise and therefore safe CRISPR-altered plants are.

Although we may associate drought problems with the developing world, America is suffering from an increasingly inadequate water supply for irrigation of its monocultures. The global commodity market demands yield stability. This is only achievable if water is sufficient during key stages in the crops' life cycle, for example maize is particularly vulnerable to any dry spell during flowering or when the kernels are swelling. Predictions of future extreme weather conditions due to climate change are a real cause for concern.

In Africa, there would appear to be much better solutions to water shortages than GM drought resistant crops: check out Practical Action's real-life work in combating drought situations in Darfur by "digging canals and creating dams to control water flow, planting trees to stabilise riverbanks, and installing terraces for growing crops ... equipping farming families with new skills to help secure their harvests" made possible by bringing together "farmers, communities, the local university, businesses and government".

Background

[1] CRISPR/Cas9 GENE EDITING - March 2016

*DowDupont bought Pioneer in 1999

SOURCES

·         Jim Gaffney, et al., August 2015, Industry-Scale Evaluation of Maize Hybrids Selected for Increased Yield in Drought-Stress Conditions of the US Corn Belt, Crop Science 55

·         Mark Cooper, et al., 2014, Breeding drought-tolerant maize hybrids for the US corn-belt: discovery to product, Journal of Experimental Botany 65:21

·         Jinrui Shi,et al., 2017, ARGOS8 variants generated by CRISPR-Cas9 improve maize grain yield under field drought stress conditions, Plant Biotechnology Journal 15

·         Drought-tolerant CRISPR maize?  Not yet - maybe not ever, GM Watch, 12.01.19

·         Laux T., et al., January 1996, The WUSCHEL gene is required for shoot and floral meristem integrity in Arabidopsis, NCBI, National Institute of Health

·         Doug Gurian-Sherman profile, https://cifileats.com/author/dgurian/

·         Bountiful harvests in North Darfur, Small World, Winter 2019

Photo: Balaram Mahalder [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]