A little extra: Genetically Modified Organisms

Authored by Sabrina Lazar - Cell Biology and Professional Writing '20

Genetically Modified Organisms (GMOs): Engineered for Good

What if you could harness the power of mutations and induce them to give a specific amino acid change, giving the organism your desired phenotype? If you had enough of these organisms on a large enough scale, how could that affect a target population, or even the ecosystem?

Technologies that enable the genetic modification of living things offer the potential for helping to tackle many of the grand challenges that society faces today: the need for sustainable energy and materials, the need for safe and secure food, the need to invent new life changing medicines, and elements of climate change to name a few. Like all new technologies, however, the application of genetic engineering comes with risk and various ethical conundrums. Therefore, considerations for responsible use of this technology must be made and the benefits and risks of any project continuously evaluated.

In this “A little extra” we discuss a promising application of genetic modification, altering plant genomes to expedite drought-tolerant crop variety growth.

The U.S. Food and Drug Administration (FDA) defines genetically modified organisms as "genetically engineered", which describes "genetic modification practices that utilize modern biotechnology." Genetic engineering refers to the process of scientists making "targeted changes to a plant’s genetic makeup to give the plant a new desirable trait."(FDA.gov)

Genetically engineered organisms, especially in crops, have actually shown to be beneficial and even life-changing for some populations. For example, to improve the lives of millions in Africa and Asia suffering from vitamin-A deficiency due to poor diets, Dr. Ingo Potrykus and Dr. Peter Beyer genetically engineered a variety of rice to provide this necessity (read more on Golden Rice here). The team was able to change the rice’s sequence to generate a novel function: making a vitamin that would otherwise not exist in the grain. In this way, the population was able to reap the benefits of GMOs (pun intended) and the vitamin-A deficiency epidemic had a solution. This is the power of genetic engineering- to change the DNA sequence and to get a new, desired phenotype.

However, what if the phenotype you are aiming for is changing a plant from diploid to haploid?

Third-year Mohamed Hisham Siddeek is working to figure that out. In his independent undergraduate research project with Drs. Anne Britt and Sundaram Kuppu, he tried to find an easier, more direct way to get plants to be haploid and true-breeding (homozygous for key traits).

In Arabidopsis thaliana, a favorite plant model organism, the CENH3 gene is involved with determining chromosome centromeres, and can cause haploid induction in plants (the mutant form causes offspring to become haploid). This haploid induction has direct applications to farming.

From left to right: Mohamed Hisham Siddeek. Small vials containing potato plants. Siddeek and a tomato plant. Dr. Sundaram Kuppu and Siddeek.

For example, let’s say a grower is interested in cultivating a GMO line specialized for drought tolerance. They want their plants to be “true-breeding”, which means that they will continue to only produce offspring with the same homozygous traits over and over again- no surprises from possible heterozygotes. However, classical techniques of achieving true-breeding lines require seven to eight generations of back-crossing the plants, taking an enormous amount of the growers’ time. If they could induce the drought-tolerant genetic change and modify CENH3 to produce haploid progeny, true-breeding lines will be achieved after just a single generation, and the grower can start seeing results faster.

This is where the project comes in: the main approach was to find a direct way to affect the CENH3 gene by changing parts of the sequence. To achieve this, the team induced several point mutations to see which could cause the following plant generations to be haploid. They found that by mating a CENH3 mutant with a wild-type plant, the progeny will be haploid and will only inherit the wild-type genes, not the mutant ones! This is important because then, in just one generation, they will be true-breeding, and if self-mated, the progeny will also share the same genotype and pass on that specific phenotype. There will be no dominant or recessive alleles in the picture to risk affecting the desired phenotype, so that specific mutant line can endure.

The CENH3 gene is conserved across all eukaryote lineages, so the goal is to explore how these results can be applied to other species of crops. In this way, we see changes as small as point mutations having the power to affect phenotype, and how this can be applied to real-world problems.

Sources:

"Golden Rice" - GoldenRice.org. http://www.goldenrice.org/Content2-How/how1_sci.php

"Food from genetically engineered plants" - https://www.fda.gov/food/ingredientspackaginglabeling/geplants/ucm461805.htm

"Arabidopsis thaliana" - TAIR. https://www.arabidopsis.org/portals/education/aboutarabidopsis.jsp

"CENH3" - Britt, Anne B, and Sundaram Kuppu. “Cenh3: An Emerging Player in Haploid Induction Technology.” Frontiers in plant science vol. 7 357. 12 Apr. 2016, doi:10.3389/fpls.2016.00357

"True-breeding" - Study.com. https://study.com/academy/lesson/true-breeding-definition-variety-quiz.html

"Point Mutations" - The Encyclopedia Britannica. https://www.britannica.com/science/point-mutation