Saturday, May 13, 2017

A GMO pineapple with a blush

A couple of months ago, I saw an article about a new "pink pineapple" that was being approved by the FDA and was a GMO. I've wanted to learn more about the variety, so in this blog post I'll be exploring the topic.

The pineapple was developed by Del Monte Fresh Produce (not to be confused with Del Monte Foods). The company plans to label it as "extra sweet pink flesh pineapple" and it will be grown in Costa Rica. In addition to pink flesh, it has a few other traits and we'll go through these one-by-one. Much of the information below came from the FDA submission documents.

Pink Flesh

To understand how the pineapple's flesh was made pink, we have to review how beta-carotene is made in plants. Beta-carotene is a pigment that has an orange color and is essential to us for vitamin A synthesis. We usually associate it with carrots. Its synthesized in plants in a multi-step process involving several enzymes. One of the intermediates in this pathway is lycopene, which is also a pigment but is bright red. Watermelon, tomatoes, and grapefruit are all fruits that are rich in lycopene. It is due to the accumulation of this pigment that the pineapple turns pink.

How was this accomplished? To make a pink pineapple, two things need to happen: a lot more lycopene needs to be made and its conversion to beta-carotene needs to be halted. To make more lycopene, the gene for phytoene synthase from a tangerine was added and was over-expressed (meaning that it was regulated in a such a way that the gene produced a lot of the phytoene synthase protein). This means that the crop can produce a lot more lycopene and beta-carotene.

However, the developers of the crop wanted lycopene accumulation without its conversion to beta-carotene. To achieve this, they silenced the lycopene β-cyclase (b-Lyc) and lycopene ε-cyclase (e-Lyc) genes in the pineapple using RNA interference. This is a naturally occurring defense mechanism that scientists have harnessed to silence genes by using the sequence of the gene itself. It triggers a pathway within the cell that chews up the RNA for the targeted gene. In this case, scientists added snippets of the b-Lyc and e-Lyc genes from the pineapple in a specific configuration. Once these snippets were turned on or expressed, it triggered the degradation of the lycopene-cyclase enzymes which are needed to convert lycopene into carotenes. Without this conversion, lycopene accumulates and the pineapple gets its beautiful pink colour.

File:Ghana pineapple field.jpg
Pineapple farm in Ghana
Image from Wikimedia Commons
By now you're probably wondering "Ok, pink pineapples are cool. But why?" Good question. The patent on the pineapple, which was published in 2013, claims "Carotenoids may contribute fundamentally to human health and in recent years there has been considerable interest in dietary carotenoids with respect to their potential in alleviating age-related diseases in humans." With a quick google search you can find tons of websites claiming that lycopene can do everything from preventing cancer to preserving bone health. Since lycopene is an antioxidant, there are a lot of websites that sell antioxidant supplements with information about the compound. However, there's little evidence supporting this.  The CDC states,"research studies have shown inconsistencies in the relation between carotenoid intake and protection from cancer." Regarding antioxidants, multiple studies have been conducted using dietary supplements and the NIH summarizes these findings by stating that "antioxidant supplements did not help to prevent disease."

Consequently, regarding this particular trait, I think that we should consider it as part of our diet rich in fruits and vegetables. As part of such a diet, it may help prevent disease. However, it's not a panacea that will cure you of your ailments. It's also a very stunning fruit from a visual perspective. Pineapple is a favorite in our house, so having a pink pineapple would be very nice to have on a fruit platter. And if that helps us eat more fruits, then why not have it as an option in our food supply? But if I'd had my choice in traits, I would have picked a pineapple that's easier to cut and handle :)

Alrighty, moving on to the next trait...

Controlled flowering

The second trait in the pineapple is controlled flowering. According to this paper: "A major limitation that afflicts pineapple growers is the phenomenon of natural flowering, which results in unscheduled fruiting. The percentage of natural induction is highly unpredictable and the incidence may vary from 0% to 100% in any given year (Kuan et al., 2005), which causes serious scheduling problems for growers and, in particular, fresh market growers".

Ethylene is a plant hormone that controls pineapple flowering, among many other things. According, to the same paper cited above, farmers currently use ethylene to "force" flowering which has been practiced for decades. This paper, which compared natural vs forced flowering, highlights that forced flowering "(a) advances flowering, (b) improves uniformity of flowering, (c) makes the harvest moment predictable, and (d) makes harvesting more uniform". The paper found that natural flowering was much more costly, but fruits produced by forced flowering were not as high quality as pineapples produced through natural flowering.

In 2006, a paper was published outlining that by silencing an enzyme involved in the synthesis of ethylene, they could delay natural pineapple flowering. The same idea was carried out in the making of the pink pineapple: an enzyme involved in the biosynthesis of ethylene (1-aminocyclopropane-1-carboxylic acid synthase) was silenced. This allows farmers to use ethylene to force flowering whenever they'd like so that all the pineapples can produce fruit at the same time.

I was left with a lot of questions about this trait, and I can only speculate on the answers. I imagine that the trait could reduce food waste on the farm. I do not know whether the need to apply ethylene increases the carbon footprint, if this is done mechanically. Ethylene ripens some fruits, however, the pineapple does not produce much ethylene to begin with, so I don't know what the silencing of ethylene synthesis does in this regards. 


The regulatory documents state that the GM pineapple is substantially equivalent to its control, with the exception of increased lycopene (which is expected) and decreased beta-carotene (which is also expected). The amount of lycopene present matched those of other fruits, such as watermelon. There were a couple of other metrics that were significantly different between the GM and the control, however, these were within the range of natural variation for the crop.

The crop will be labeled as "“Extra Sweet Pink Flesh Pineapple”. According to this article, the regular Del Monte pineapple is labeled as "extra sweet", so the pink one isn't any sweeter than "normal".


So, will I buy this pineapple? If I were to guess, I'd say that the company started working on this pineapple about 10 years ago when the antioxidant craze was at its peak. But 10 years later, that craze has fizzled away. I think the company has a pink pineapple that's visually beautiful, but has no real health benefit. I'd buy this pineapple if it doesn't cost more than usual. I'd like to know whether the controlled flowering trait reduces food waste, because if that's the case it would be worth paying a small premium. Otherwise... meh?

Man, I learned a crap ton about pineapples by writing this post... Let me know if you have any questions below.

Friday, April 7, 2017

Plants vs Zombies: The GMO Edition

I know. It's been a while... Things are a bit rough. I've written a few pieces over on Medium, if you want to check them out.

So, in this blog post, I wanted to write about "superweeds", what they are, how they're related to GMOs, and some misconceptions about them. The first thing to know is that "superweed" is not a scientific term. Searching through the NIH's database of scientific publications, I only found one paper with the term "superweed", and it's a commentary, not a research article. Yet "superweed" is a term used ALL the time on websites that lobby against GMOs, like this article entitled "Superweeds: A Frightening Reality" written by the "Just Label It" campaign. 

My understanding of the term and its use is that "superweed" describes weeds that don't get killed by herbicides. They don't grow faster or stronger than other weeds. They arise due to selective pressure from the herbicide. Spouse, don't freak out. I'm going to explain this to you in detail, using your favoritest of analogies: zombies.

Imagine that the zombie apocalypse takes places tomorrow and is caused by a virus. Imagine that 1% of the human population had some sort of mutation in their DNA that made them resistant to the virus. That means that only 1% of the human population would survive. It also means that 100% of surviving humans are resistant to the zombie virus. The surviving humans would mate with one another and from that point onward, all humans would have the mutation that makes them resistant to the zombie virus (assuming, of course, that humans wouldn't mate with zombies... That would make a crazy scifi movie...). You could say that the surviving humans are "superhumans". 

But did the zombie virus cause the mutation? No, it did not. The superhumans were there all along. The zombie virus placed pressure on the system, and the mutant humans were "selected" because they lived.

A mutation that's shared by 1% of humans is a relatively large number of people. Why would so many humans have it? Well, maybe it makes humans resist other viruses too and gives them some sort of advantage. Or maybe at some point throughout the course of our evolution, there was a similar virus that wiped out a good chunk of our population, and our ancestors (human or not) survived because of the mutation. But since there hasn't been a zombie virus since that ancient plague, we haven't really needed that mutation. With no selective pressure, it may be why most humans no longer have the mutation.

But let's assume that there has never been any pressure for this mutation to remain in our population. In that case, very, very, very few humans, if any at all, would have the mutation making them resistant to the zombie virus. It would be pure luck if a human had that particular mutation, since mutations happen randomly in our DNA.Given how our species reproduces, there would need to be two humans who won this genetic lottery at the same time in history and in close proximity of one another, so that they could mate and have superhuman offspring. Otherwise, humans would get wiped out.

Pretty unlikely, right? Still, the zombie virus did not cause the mutation. 

Now, if the zombie apocalypse were part of a plan of some evil mastermind, the villain's best chance of success would be to release two viruses into the environment at the same time: let's say a zombie virus and a flesh-eating virus. The odds of a single individual or population being resistant to both viruses would be extremely, extremely, rare. 

So, that's probably as far as I can take the zombie apocalypse analogy.

Weeds that are resistant to herbicides are bound to arise, even with the best of herbicides. The same is true of antibiotic resistant bacteria. Given enough time, they'll be found. If a herbicide is well designed, no existing weeds will be resistant to it (i.e, in our analogy, a good herbicide wouldn't leave 1% of weeds behind). This is tricky, because there are so many different weeds to combat. But, the herbicides don't cause the resistance. Neither do antibiotics. Resistant bugs and resistant weeds win the genetic lottery and thrive. Since bacteria don't need to mate, it's even easier for an antibiotic resistant bug to spread.

Weeds that evolve to become resistant to herbicides have existed WAY before GMOs, because we've been using herbicides in agriculture before GMOs were commercialized. There are even weeds that have evolved to look like crops, so that they can evade hand-weeding. It is for these reasons that farmers are encouraged to practice good management to control weeds. This means that they're encouraged to rotate crops, to use herbicides that impact the plant in different ways, and to use mechanical methods to kill weeds, too. And although we may not like it, using two different herbicides makes sense and ag companies are starting to introduce GMOs with the ability to resist two herbicides. The odds of getting a weed that is resistant to both herbicides is much less, but again, it's only a matter of time before one arises.

Glyphosate has been a pretty good herbicide in terms of the development of herbicide resistant weeds. But because it was used on so many acres of land, the odds of finding a weed that "won the genetic lottery" increased. Consequently, glyphosate-resistant weeds have been identified in many areas and are a problem for some farmers. 

The term "superweed", when used in the context of the GMO debate, evokes imagery of a weed that's about to take over the planet. As I highlighted at the beginning of this piece, you'll see references to superweeds all over anti-GMO websites. Herbicide resistant weeds are a problem in agriculture, but it's far from being unique to GMO crops. So ask yourself why such language is being used, and be aware if its because the website in question is trying to manipulate your emotions.

For more on this topic, I encourage you to read this 2-page summary on superweeds or to look at this website. And follow @wyoweeds and @LynnSosnoskie on twitter (can't stress this enough).