Increasing stress tolerance in crops
Crops can experience an assortment of environmental stresses throughout their entire development, including drought, salinity, prolonged rain-fall and extreme temperatures to name a few. Their ability to tolerate or adapt to these stresses, as well as their inability to do so, is a very multifaceted phenomenon. However, epigenetic technologies could be used effectively to down regulate the genes related to stress responses. For instance, researchers investigating drought tolerance in rice at various developmental stages have found that RNAi mediated disruption of certain genes improves the crops’ ability to extract soil water and avoid dehydration. This process which inhibits gene expression occurs without adversely affecting plant architecture, growth or development 1.
In a different study, scientists discovered that by epigenetically modifying or “turning off” the gene MSH1 in crops like soybean and sorghum, they were able to simulate high stress exposure. Then, after reactivating the gene and crossbreeding with unaltered plants, they found that the hybridized plants had enhanced growth, biomass and yield. The genes themselves did not change in this experiment, only the way they were expressed changed. This is different from transgene-mediated modification, which is a controversial genetic modification because it involves taking a segment of DNA from one organism and introducing it to a different organism. In addition, the researchers found that the transformation was successful by the second generation, rather than by the 10th generation or more which is common for most genetic modifications to catch on. Although scientists are still learning how to epigenetically breed more varieties of stress resistant plants, given the sense of urgency to feed a growing population, the prospects for this new approach are appealing and should be further explored 2.
Raising nutritional value in crops
Commercially grown food is produced in far greater quantities today than was 50 years ago, yet the overall nutritional value of these crops has declined. Studies show that modern crops contain 10 to 25 percent less protein, iron, zinc, calcium, vitamin C and other important nutrients than the lower yielding crops of the past 3. Unfortunately, this only adds to the prevailing malnutrition affecting billions of people worldwide, primarily the poor, who do not have access to adequate and diverse food choices.
In many developing countries, a significant portion of the population relies on one or more of a staple crop like rice, corn or wheat for nutrition. Though important sources of calories and carbohydrates, these crops do not contain enough protein or micronutrients for proper cellular development and sole reliance on them for diet can lead to major health conditions. For example, vitamin A deficiency is common and widespread in developing countries, contributing to blindness and high mortality rates 4. Other deficiencies like zinc, iron and folate have been linked to anemia, low birth weight and genetic disorders. While the practice of fortifying certain staple foods has been successful over the years, it is not always achievable or accepted in certain countries 5.
Enhancing a crop’s ability to acquire added nutrients may be more feasible and effective in the long run. Currently, research using RNAi technologies to modify gene expression at a specific stage of development is being used to improve the nutritional value of plants. In cotton, it has been applied to develop lines with low gossypol levels, a protective toxin naturally found in the cottonseed. By suppressing the production of this toxin, the cottonseed becomes a viable source of protein and calories that can be used for human or livestock consumption. This is worthwhile since cotton is produced in abundance for its fiber and the seed is frequently underutilized.
In wheat and other grains, RNAi constructs have been designed to suppress the genes that promote starch levels. The results are grains with higher amylose content which is beneficial for lower blood sugar and cholesterol. As well, RNA applications have shown to improve carotenoid and flavonoid levels in tomatoes and lower the natural caffeine levels in coffee without affecting plant growth 6.
Nutrient-rich foods are beneficial to everyone, but more so to groups that are vulnerable to micronutrient deficiencies. Further study involving epigenetic mechanisms to enhance crop nutritional content is desirable and necessary. It will allow us to better understand overall plant metabolism and consequently help us to improve upon human and animal health and well-being.
Improving pest and disease resistance in crops
Plant diseases and pests have been known to lay waste to entire harvests. The Irish potato famine of the 1840s caused by a simple fungus-like microorganism was so devastating it caused widespread starvation and forced many to uproot their families and leave the country 7. Western and Northern Africa are continuously invaded by swarms of locusts that destroy all kinds of vegetation in their path, often claiming large hectares of staple crops and devastating the economy of rural communities 8.
Some farmers employ pesticides to improve crop yield, yet pesticides come with a cost. The quality of the food is tainted by the chemicals and the environment endures contamination, not to mention, the harmful effects on human health after consumption. Instead of pesticides, plants could be epigenetically triggered to naturally fend off pests and disease, as many plants are known to adapt to their environment. In fact, some can produce natural defense compounds against herbivore attacks.
In a study investigating epigenetic mechanisms involved in plant defense response, in particular siRNAs, researchers found that tomato plant exposure to caterpillar herbivory triggered a chemical reaction. This defense response was then seen in future generations that had not been exposed to the pest 9. In a related study, Arabidopsis plants deliberately infected with benign bacteria were able to produce offspring that showed resistance or had immunity to the bacteria 10. While these findings imply that siRNAs may play a role in plant memory, they also demonstrate opportunity for use in other crops, especially those grown in areas with heavy pesticide use. Strategies to utilize these transgenerational plant memory responses could prove to be cost effective, better suited for the environment and lessen the need for GMOs to strengthen crop production.
What lies ahead?
Perhaps someday, we won’t need concerts to raise money to end hunger. A wonderful thought, I know. But, we do have the knowledge and we’re learning more each day on how to combat hunger and malnutrition by improving crop production. And, thanks to ongoing efforts, the science of epigenetics is proving to be a very promising route to explore. By naturally modifying plant gene expression without altering the genome, epigenetic processes could provide farmers better yields, higher quality food, and more stress tolerant crops. All of this is possible and would likely cost less, happen in a shorter time, and not be damaging to the environment. In the foreseeable future, I believe we shall see a strong presence of epigenetics, not only in crop improvement, but in food production, nutrition and human health. With more research, the field of epigenetics may bring to the table real results that will help to cover the growing food demand of the world.
- Manavalan, LP. et al. (2012). RNAi-mediated disruption of squalene synthase improves drought tolerance and yield in rice. J Exp Bot., 63: 163–175. ↩
- Jasa, L. Nebraska: Plant Scientists Hoping to Utilize Epigenetics. 2 Jan 2013. Web. ↩
- Worldwatch Institute. Crop Yields Expand, but Nutrition Is Left Behind. 2013. Web. ↩
- International Service for the Acquisition of Agri-biotech Applications (ISAAA). The Ideal Diet: Sufficient and Balanced. Pocket K No. 27: Biotechnology and Biofortification. 2015. Web. ↩
- Samaniego-Vaesken, M. et al. (2012). Vitamin food fortification today. Food Nutr Res., 56, 10.3402/fnr.v56i0.5459. ↩
- Angaji, SA. et al. (2010). Application of RNA interference in plants. Plant Omics Journal, 3:77-84. ↩
- Wikipedia. Great Famine (Ireland). Web. ↩
- United Nations Environment Program. Pests and invasive species in Africa. The Encyclopedia of Earth. 13 Apr 2007. Web. ↩
- Coombs, A. Plants have a memory of pests that spans generations. Ars Technica. 29 Feb 2012. Web. ↩
- Rasmann, S. et al. (2012). Herbivory in the Previous Generation Primes Plants for Enhanced Insect Resistance. Plant Physiol., 158(2): 854-863. ↩