And then there are GM organisms designed to appeal directly to the final consumers. One of the first will be the Arctic Apple, which does not brown rapidly after it is cut or bitten into. This is thanks to the insertion of genes from other apple varieties that produce lower than usual levels of polyphenol oxidase, a key enzyme in the chain of biochemical events that cause browning.
“My wife and I are apple growers ourselves. We were concerned because apple consumption has been declining,” says Neal Carter, president of Okanagan Specialty Fruits in Summerland, British Columbia, the developer of the Arctic Apple. Carter says that apples are losing ground in the supermarket to carrots and other fresh produce that is sold in bags, cleaned, sliced and ready to eat. Making apples that could be processed in such a way without browning could be a real boon for the industry. And if the apples are received well, says Carter, Arctic avocados, pears and even lettuce could be next.
Much of the genetic-modification work so far has been achieved with relatively crude but established techniques, such as a 'gene gun' that fires gold nanopellets coated with DNA from other organisms into the cells of the target plant, which incorporate the DNA at random sites in the genome. But new tools offer unparalleled precision in editing genes. For example, enzymes called transcription activator-like effector nucleases (TALENs) and zinc-finger nucleases (ZFNs) can cut DNA at specific points chosen by the experimenter. By controlling how this break is repaired, it is possible to introduce mutations, single-nucleotide changes or even whole genes at precise sites, says Dan Voytas, who works with such techniques at the University of Minnesota in St Paul. “We can do precise insertion so we know where in the chromosome the foreign gene resides.” This allows researchers to put the new gene in a spot in the genome where its expression is optimal, and reduces the risk of disrupting the plant's genome in undesirable ways. Voytas's group has already shown that tobacco plants can be modified with ZFNs to introduce herbicide resistance. Other groups have added herbicide resistance to maize (corn) with ZFNs or have used TALENs to snip out the gene in rice that confers susceptibility to bacterial blight.
But Voytas says the “real power” of these techniques lies in the ability to confer new traits by modifying native plant genes. For example, rather than engineering plants to withstand dry conditions by incorporating genes from drought-tolerant bacteria (see Nature 466, 548–551; 2010), researchers could adjust the multiple native genes that help plants to survive drought. “Really, the next stage of the development of the technology is to go in and to tweak multiple genes,” says Voytas.
Derek Jantz, co-founder of Precision BioSciences, a biotechnology company based in Durham, North Carolina, is also excited about working with a plant's own genes. For example, all plants have an analogue of the bacterial EPSPS gene that is inserted into Monsanto's Roundup Ready crops. It should be possible to create similar herbicide resistance by editing a plant's own version, rather than bringing in an external gene.
Like other researchers in the genetic-modification industry, Jantz declines to talk about specific research projects because of commercial confidentiality. But in general terms, he says, “what we're trying to do is take advantage of the wealth of functional genomics data that is becoming available”.