When speaking of spiciness in science, we use an entirely different term that perhaps holds a slightly altered connotation in common language: pungency. It is this that refers to the sensation of heat after consumption and how intense and long-lasting that effect is on the average consumer. And there is no other quintessential aspect of spicy cuisine than the chili pepper of the Capsicum genus, though all of its fellow species in the genus are similarly hot.
The Field of Pepper Research
The members of this group have long since spread around the globe and been incorporated into the food traditions of many a differing culture. At the same time, there has also been a competition among pepper cultivators to create an ever more spicy version of the food, to be able to hold the crown of most unedible foodstuff in the world, if you mind my cheek. But lately the process of doing so has become complicated due to growers reaching the conceivable limit of likelihood of being able to directly breed an even greater level of pungency. So there have been hopes that the in-depth sequencing of the chili pepper genome would unveil some secrets of heat production and enable other methods of furthering the goal.
The sequenced genome has likely done that, yes, but it has also opened up other avenues for spreading pungent flavors to new vistas. There is additionally the fact that the other secondary metabolites of peppers are highly beneficial for human health, such as the inclusion of vitamins, antioxidants, carotenoids, and even anti-inflammatory and anti-tumor compounds. And all of these are contained in the fruits, so there isn’t a need to be concerned over other parts of the plant.
As another scientific note, it is not entirely clear why and how peppers use these odorous and often offensive spice flavors in the wild, as their fruits still need to be dispersed by animal consumption. One hypothesis, referred to as the directed deterrence hypothesis, is that the capsaicinoids are able to selectively impact pests that would not serve the plant’s dispersal needs, while not meaningfully harming or annoying the proper dispersal subjects. If this is indeed the case, then it shows just how important a role secondary metabolites like this may have in mutual evolutionary interactions between species.
Not Pepper, But Tomato?
A research team in Brazil decided to raise the question: what if we made tomatoes spicy too? The pepper and tomato families are closely related, having split from each other a mere 19 million years ago. And their genomes have not changed all that much since that time, with them retaining the same number of chromosomes and biological features. Though tomatoes do have the distinction of being the larger producer and of growing in various climates. A benefit of this suggestion is that tomatoes are an incredibly well studied species, being a model organism in their own right, and are a major horticultural crop around the world. So, engineering tomatoes into a capsaicinoid production machine isn’t out of the question.
The first step is to understand the quantity of these compounds, the pathways through which they are made, and also what region of the fruit they are stored in. The answer to those questions are, in order, 23 types, two primary biochemical pathways, and the fruit placenta along with specific intracellular compartments for each cell. One of the genetic routes is the phenylpropanoid pathway, which starts with the amino acid phenylalanine and eventually creates the compound vanillylamine. The alternative route is the branched-chain fatty acid pathway that takes the amino acid valine and makes 8-methyl nonenoic acid. Enzymes then combine these two end products to form capsaicin. The other capsaicinoids are produced by changing vanillylamine through interactions with fatty acids and then combining with the other end product again.
An indeed interesting thing to note is that tomatoes also have the fully functional phenylpropanoid pathway, but conversely don’t have active the needed genes for converting valine in the other pathway. The genes are there, but not set up in the right format. Research into how pungency is lost in mutations with sweet peppers has given some clue in how spiciness can be lost through changes in this pathway, thus showing ways it might be corrected in tomatoes. What has been revealed is that levels of pungency are regulated by how much certain genes are transcribed and it does appear that tomatoes have significantly lower activity levels for some key genes in this production pathway.
Therefore, using any number of potential genetic engineering tools to upregulate several of these required genes could be all that is needed to activate true spiciness. Alternatively, those same tools could be used to replace the promoter sequences for these genes and have their transcription be increased that way. Other, stronger promoters in the tomato genome could be used for this purpose and, thus, create a cisgenic product. Such a thing might be useful to avoid onerous regulations of transgenic plants in certain parts of the world.
Take Up The Quest
And that’s where things stand right now. The research team was not actually conducting such an experiment, but just investigating the feasibility for it to be done. Their conclusion is full speed ahead on the spicy tomatoes train. It is completely possible to attempt to activate the capsaicin pathways in tomatoes and while there may be some as of yet unknown hurdles in doing so, there’s no reason to not try. Since tomatoes are a hot commodity in themselves, the high sales and consumption of a product like that are virtually guaranteed, so there is no cost benefit restriction on the research.
All we need now is some group of scientists with the guts and verve to take on that challenge, to bring instantly spicy salsa to all the world. I’m hungry now, how about you?
Photo CCs: Chillies (3347274146) from Wikimedia Commons