The previous issue of the IPM Chronicle discussed recent findings from the National Academy of Sciences related to the safety of genetically engineered crops on human health and the environment. Now, the discussion turns to the recent developments and the potential benefits of such modern techniques to produce genetically modified crops. In order to fully understand the advanced techniques developed to design crops, it’s essential to understand past crop breeding methods.
History of Plant Breeding
Ever since humans domesticated plants to produce food about 10,000 years ago, they were continuously selected for desirable traits that occurred naturally. The field of classical plant breeding through cross-pollination witnessed rapid growth following the famous pea-plant experiments of Gregory Mendel who outlined the “rules of genetics” in the late 1800s.
As scientists began to understand that physical traits expressed was by virtue of genetic information, crude mutagens (agents that can alter the genetic sequence), such as radioactive rays or certain chemicals, were used to induce mutations to generate new varieties shortly after World War II. This was followed by plant tissue culture to induce and select desirable expressions. However, most of these methods were time consuming, cumbersome and often times dependent on trial and error.
An understanding of DNA structure and function in the mid-1960s paired with the vast body of scientific literature that followed this fundamental discovery accelerated this discipline during the past five decades. As a result, scientists were able to genetically engineer crops and introduce the genes of foreign, and often unrelated, species to express certain desirable traits, such as herbicide tolerance (e.g., Roundup-Ready crops) and their ability to kill certain insect pests (e.g., Bt corn). They were referred to as transgenic crops since the technique involved the introduction of foreign genes into the genome of a crop species. Such transgenic crops have been widely adopted but have been under public and regulatory scrutiny. The regulatory processes became a hurdle in the rapid development of transgenic crops.
Recent advances in molecular biology have made it possible to edit the genes within a particular species as opposed to introducing those from another species. One of the major benefits of gene editing is that improved varieties can be developed and released without much regulatory interference since this practice is similar to older methods, such as classical breeding, mutagenesis or plant tissue culture, which were not regulated.
Several gene editing techniques are being developed by scientists. These techniques employ different agents collectively referred to “Sequence Specific Nucleases” to cut and customize gene sequences to achieve desirable end results. The four major classes of SSNs include clustered regularly interspersed short palindromic repeats associated with Casnuclease 9 (CRISPR/Cas9); meganucleases; transcription activator-like effector nucleases (TALENS); and zinc finger nucleases (ZFNs). CRISPR/Cas9 is used most widely by scientists because of its simplicity for DNA targeting and gene editing.
Gene editing is promising and is considered to be less invasive compared to transgenic crops.
Recently, a mushroom variety that can resist browning was developed by Penn State using this technology. It has also been considered in the development of golden rice capable of synthesizing vitamin A that has the potential to treat blindness associated with children nutritionally deprived of the vitamin. Although possible through a transgenic hybrid, its development and cultivation were hindered.
While regulation of gene editing technology is less stringent, widespread adoption and public acceptance is yet to be documented. However, companies are rapidly using these new tools to generate crops that are drought-, fungal disease- and herbicide-resistant. They’re also being modified to protect against other agricultural pests, such as insects and weeds.