Work in the genetic resources program at the International Center for Tropical Agriculture (photo on Flickr by CIAT/Neil Palmer).
Are promising genetically modified food crops doomed to stay in greenhouses? What about crops whose bits (of bits) of their genomes have been ‘precision edited’ with the help of new genome engineering tools (Talens and Crispr) without the introduction of foreign genes?
These are exciting times for geneticists, who are reaching the holy grail of genetic engineering. But will it make a difference to feeding our growing, hotter, hungrier world?
‘. . . Although agricultural productivity has improved dramatically over the past 50 years, economists fear that these improvements have begun to wane at a time when food demand, driven by the larger number of people and the growing appetites of wealthier populations, is expected to rise between 70 and 100 percent by midcentury. In particular, the rapid increases in rice and wheat yields that helped feed the world for decades are showing signs of slowing down, and production of cereals will need to more than double by 2050 to keep up. If the trend continues, production might be insufficient to meet demand unless we start using significantly more land, fertilizer, and water.
Climate change is likely to make the problem far worse, bringing higher temperatures and, in many regions, wetter conditions that spread infestations of disease and insects into new areas. . . .
‘The promise that genetically modified crops could help feed the world is at least as old as the commercialization of the first transgenic seeds in the mid-1990s. The corporations that helped turn genetically engineered crops into a multibillion-dollar business, including the large chemical companies Monsanto, Bayer, and DuPont, promoted the technology as part of a life science revolution that would greatly increase food production. So far it’s turned out, for a number of reasons, to have been a somewhat empty promise.
‘To be sure, bioengineered crops are a huge commercial success in some countries. The idea is simple but compelling: by inserting a foreign gene derived from, say, bacteria into corn, you can give the plant a trait it wouldn’t otherwise possess. Surveys estimate that more than 170 million hectares of such transgenic crops are grown worldwide. In the United States, the majority of corn, soybeans, and cotton planted have been engineered with a gene from the soil bacterium Bacillus thuringensis—Bt—to ward off insects or with another bacterial gene to withstand herbicides. Worldwide, 81 percent of the soybeans and 35 percent of the corn grown are biotech varieties. In India, Bt cotton was approved more than a decade ago and now represents 96 percent of the cotton grown in the country. . . .
So far, the short list of transgenic crops used directly for food includes virus-resistant papaya grown in Hawaii, Bt sweet corn recently commercialized in the United States by Monsanto, and a few varieties of squash that resist plant viruses. That list could be about to grow, however.
‘. . . Opponents worry that inserting foreign genes into crops could make food dangerous or allergenic, though more than 15 years of experience with transgenic crops have revealed no health dangers, and neither have a series of scientific studies. . . . The most persuasive criticism, however, may simply be that existing transgenic crops have done little to guarantee the future of the world’s food supply in the face of climate change and a growing population. . . .
‘Developing crops that are better able to withstand climate change won’t be easy. It will require plant scientists to engineer complex traits involving multiple genes. Durable disease resistance typically requires a series of genetic changes and detailed knowledge of how pathogens attack the plant. Traits such as tolerance to drought and heat are even harder, since they can require basic changes to the plant’s physiology.
‘Is genetic engineering up to the task? No one knows. But recent genomic breakthroughs are encouraging. . . . [A]dvances in molecular biology mean that genes can be deleted, modified, and inserted with far greater precision. In particular, new genome engineering tools known as Talens and Crispr allow geneticists to “edit” plant DNA, changing chromosomes exactly where they want.
Plant breeding “is not the art of shuffling genes around,” [Walter] De Jong explains. “Basically, all potatoes have the same genes; what they have is different versions of the genes—alleles. And alleles differ from one another in a few nucleotides.
If I can edit the few nucleotides, why breed for [a trait]? It’s been the holy grail in plant genetics for a long time.”. . .
Talens, one of the most promising of these genome engineering tools, was inspired by a mechanism used by a bacterium that infects plants. Plant pathologists identified the proteins that enable the bacterium to pinpoint the target plant DNA and found ways to engineer these proteins to recognize any desired sequence; then they fused these proteins with nucleases that cut DNA, creating a precise “editing” tool. A plant bacterium or gene gun is used to get the tool into the plant cell; once inside, the proteins zero in on a specific DNA sequence. The proteins deliver the nucleases to an exact spot on the chromosome, where they cleave the plant’s DNA. Repair of the broken chromosome allows new genes to be inserted or other types of modifications to be made. Crispr, an even newer version of the technology, uses RNA to zero in on the targeted genes.
With both Talens and Crispr, molecular biologists can modify even a few nucleotides or insert and delete a gene exactly where they want on the chromosome, making the change far more predictable and effective.
‘One problem with conventional genetic engineering techniques is that they add genes unpredictably. . . . What if you could precisely target spots on the plant’s chromosome and add new genes exactly where you want them, “knock out” existing ones, or modify genes by switching a few specific nucleotides? The new tools allow scientists to do just that. . . .
‘With both Talens and Crispr, molecular biologists can modify even a few nucleotides or insert and delete a gene exactly where they want on the chromosome, making the change far more predictable and effective.
‘One implication of the new tools is that plants can be genetically modified without the addition of foreign genes. Though it’s too early to tell whether that will change the public debate over GMOs, regulatory agencies—at least in the United States—indicate that crops modified without foreign genes won’t have to be scrutinized as thoroughly as transgenic crops. That could greatly reduce the time and expense it takes to commercialize new varieties of genetically engineered foods. And it’s possible that critics of biotechnology could draw a similar distinction, tolerating genetically modified crops so long as they are not transgenic.
‘Dan Voytas, director of the genome engineering center at the University of Minnesota and one of Talens’s inventors, says one of his main motivations is the need to feed another two billion people by the middle of the century. . . .
‘Rewriting the core workings of a plant is not a trivial task. But Voytas says Talens could be a valuable tool—both to identify the genetic pathways that might be tweaked and to make the many necessary genetic changes.
The pressure to help feed the growing population at a time when climate change is making more land marginal for agriculture is “the burden that plant biologists bear,” Voytas says.
‘. . . We need to have crops that are better at dealing with hot climates.” . . . It’s possible that plants are simply hardwired to shut down at temperatures above 30 °C. Indeed, Schlenker says he’s not convinced that crops can be engineered to adapt to the increased frequency of hot days, though he hopes he’s wrong. . . .’
Read the whole article by David Rotman in MIT Technology Review Magazine: Why we will need genetically modified foods, 17 Dec 2013.