Genetically Engineered Spicy Tomatoes?

Everyone knows that the two main ingredients in salsa are tomatoes and chili peppers. But what if you could combine those two ingredients into one? Not only would this invention make preparing salsa a whole lot easier, but it would also represent a major scientific breakthrough.

Genome (or gene) editing is a group of technologies that gives scientists the ability to change an organism's DNA—genetic material can be added, removed, or altered at specific locations in the genome. In fact, thanks to developments in genetic engineering, scientists are able to genetically modify crops, such as grains and fresh produce, in order to yield certain desired traits, which can range from larger size to enhanced taste. A team of plant physiologists in Brazil and Ireland recently explored the possibility of engineering spicy tomatoes using gene editing. But how exactly is this possible?

It all begins with capsaicinoids: the molecules responsible for the spiciness in chili peppers. Capsaicinoids are also used as low-risk painkillers in creams for arthritis and are the main component in pepper spray. However, there are many agricultural challenges in chili pepper cultivation, such as intolerance to elevated temperatures and susceptibility to viruses. Moreover, capsaicinoid levels are highly dependent on environmental conditions, so the pungency of the peppers can differ even within the same species.

In response to these difficulties in pepper cultivation, a team of plant physiologists led by Agustin Zsögön at the Federal University of Viçosa in Brazil proposed using gene editing to engineer spicy tomatoes. They were aware that the chili pepper and tomato shared a common ancestor before separating 19 million years ago. So when comparing the chili pepper genome to that of the tomato, it was no surprise that the tomato plant contained all the necessary genes for capsaicinoid production in its genome; the genes were just inactive. Furthermore, the tomato is a model organism that has already been the subject of several genetic modification studies: the first genetically modified (GM) crop was a delayed-ripening tomato that was introduced in 1994 as “Flavr Savr.” Another type of genetically modified tomato is one that contains antifreeze proteins from coldwater fish. This was meant to increase the tomatoes’ tolerance to frost, a key culprit that compromises the quality of fruits and vegetables through damaging effects of ice crystal growth within frozen tissue.

Zsögön and his team were hoping to create another GM tomato, one with capsaicinoids in larger quantities.

According to Zsögön, two gene-engineering strategies could be used in tandem to activate capsaicinoid biosynthesis in the tomato. One is the use of transcriptional activator-like effectors (TALEs), a suite of proteins secreted by pathogenic Xanthomonas spp. bacteria when they infect plant hosts, to upregulate the expression of genes necessary to make capsaicinoids. It remains to be determined whether the transcript levels achieved will be sufficient for the capsaicinoid pathway to be functional because the expression could either be too low and thus insufficient to activate the capsaicinoid pathway, or too high, which could trigger gene silencing in which previously active genes are rendered inactive.

The second strategy is using gene engineering for the targeted replacement of promoters, which are DNA sequences that determine where transcription of a gene begins. The feasibility of this method has already been demonstrated in tomatoes. Promoter regions of the inactive genes in the capsaicinoid pathway could be replaced to produce transcriptionally active genes. What remains to be determined, however, is if the genes are fully functional, biochemically active, and catalyze the appropriate reactions. By utilizing both of these strategies, Zsögön and his team believe that a “hot” tomato containing active capsaicinoid genes can be engineered.

However, with genetic engineering comes ethical questions. Multiple concerns have been raised about GM crops, the first being the potential harm to human health. Many are worried about what toxins they would ingest by consuming GM crops. To add to this concern, the effects of GM crops on the human body are not well characterized because the crops are generally tested on animals (another ethical issue by itself).

Second, environmentalists believe that GM crops could cause potential damage to the environment because of increased herbicide use, pleiotropy, or the alteration of DNA that can change a cell’s composition, and contamination. GM crops can cross-pollinate with wild and non-GM plants, contaminating wild plants and affecting their natural genetic makeup, which can seriously compromise any organic or non-GM farming system.

Next, GM crops could have a negative impact on traditional farming and promote excessive corporate dominance. Specifically, farmers traditionally save their seeds from previous harvests to reuse them and save on costs. With the advent of GM seeds, however, businesses have increasingly bought out seed companies and control seed availability, forcing farmers to buy their GM seeds.

Fourth, one major factor that has interrupted the success of many GM crops is high production costs. For example, Golden Rice was invented by scientists from Syngenta, an agricultural chemical company, to help malnourished people suffering from Vitamin A deficiency. However, this type of GM rice took almost 20 years to produce and cost millions of dollars. In fact, Flavr Savr never made it to grocery stores because of its high production costs.

Due to ethical questions, there hasn’t been an update on the progress of engineering spicy tomatoes from Zsögön and his team. It cannot be denied that their proposal is beneficial for making capsaicinoids easily and in larger quantities and can significantly help businesses that use capsaicinoids in their products. While the thought of eating spicy tomatoes is certainly appealing, there are many concerns regarding GM crops that remind us to step back and evaluate the effects of genetically modified organisms, including spicy tomatoes.

Nevertheless, the fact that spicy tomatoes could even be possible is an indicator of how developed gene editing has become, and it could pave the way for engineering other biosynthetic pathways using the tomato fruit as a biofactory.