Bacteria and Tubers and GMOs, OH MY!

Howdy Cowboys and Cowgirls.

IMG_6679

It’s been a while since I’ve checked in on this little-blog-of-mine. I apologize for my extended absence, I’m still in recovery-mode from my crazy-cross-country moving extravaganza!

One of these things is not like the other...
One of these things is not like the other…

Way back when I started this blog, I had a semi-regular feature called “Things I Like Thursday,” where I shared whatever tripped my trigger during that particular week.

My trigger is usually tripped by Elvis and/or oatmeal.
My trigger is usually tripped by Elvis and/or oatmeal.

This Thursday I think I’d like to talk about a nifty research article that came out a few weeks ago that covers topics near and dear to my heart: bacteria, genetic engineering, and carbohydrates.

Specifically, sweet potatoes
Specifically, sweet potatoes

The manuscript, which was published in PNAS, provides evidence that human have been cultivating transgenic sweet potatoes since ancient times, WAY before Monsanto was even an inkling of an idea in the fiery depths of Mordor some corporate boardroom.

Third quarter profits are looking STRONG
Third quarter profits are looking STRONG

The authors looked at genomic sequences from 291 cultivated sweet potatoes and found evidence for (gasp!) genetic modification! Sweet potatoes express genes from a DIFFERENT ORGANISM! Some malevolent force created transgenic tubers all over the world!

Cue
Cue “Psycho” Music

It turns out that cultivated sweet potatoes chromosomes contain genes from an amazing bacteria named Agrobacterium rhizogenes.

The plant genes are orange, the bacteria genes are green. (Source: Kyndt et al. PNAS, 2015; http://www.pnas.org/content/112/18/5844)
The plant genes are orange, the bacteria genes are green. (Source: Kyndt et al. PNAS, 2015; http://www.pnas.org/content/112/18/5844)

Agrobacterium is the original gangster when it come to genetically modifying plants. Bacteria within genus Agrobacter cause Crown Gall Disease; they inject a chunk of their own DNA into plant cells to trick the poor unfortunate foliage into making a happy food-filled tumor-home, inside which the bacteria grow like gangbusters.

Pictured: Bacteria-filled plant tumors.  Source: (Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org - See more at: http://www.forestryimages.org/browse/detail.cfm?imgnum=1436062#sthash.wwUN8Iaa.dpuf)
Pictured: Bacteria-filled plant tumors.
Source: (Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org – See more at: http://www.forestryimages.org/browse/detail.cfm?imgnum=1436062#sthash.wwUN8Iaa.dpuf)

Human beings learned everything we know about making GMOs from Agrobacterium tumefasciens. Therefore the fact that we see bacterial DNA inside a plant genome is not necessarily surprising. Bacterial genomes are prodigiously promiscuous. Single celled organisms swap genes like pokemon cards, and evidence continues to mount that multi-cellular organisms, like ticks, are in on this genetic modification party.

Source: Plos Biology article Does Medicine without Evolution Make Sense? MacCallum CJ (2007) PLoS Biol 5(4): e112. doi:10.1371/journal.pbio.0050112
Source: Plos Biology article
Does Medicine without Evolution Make Sense?
MacCallum CJ (2007) PLoS Biol 5(4): e112. doi:10.1371/journal.pbio.0050112

Earlier studies found evidence that tobacco plants carry around some Agrobacterium genes from an ancient transfer event. Bacteria have been genetically modifying plants for their own purposes since before humans emerged. The most surprising feature of this work is that the bacterial genes were only found within CULTIVATED sweet potato species, not in the plants’ wild relatives. The implication is that during the domestication process, human beings somehow selected for sweet potatoes harboring bacterial DNA. In other words, even though we didn’t MAKE sweet potatoes GMO in the first place, we contributed to their prevalence by propagating a transgenic organism since paleolithic times.

Sweet potatoes are totally Paleo, right?
Sweet potatoes are totally Paleo, right?

I mostly highlight this study as an opportunity to raise some pesky questions about how we define that big-scary term “GMO.” Modifications to genomes come in many different shapes and sizes. As I’ve mentioned before, transgenic organisms contain DNA from multiple species. Our cultivated sweet potatoes are clearly transgenic.  Does it matter if a bacteria or a human did the mixing and matching?

I make GMOs all day
I make GMOs all day
I also make GMOs all day... (Source: Matthysse et al. J Bact, 1981; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC217308/)
I also make GMOs all day…
(Source: Matthysse et al. J Bact, 1981; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC217308/)

I’d argue that a sweet potato with A. rhizobia alleles is WAY less scary than Round Up Ready corn. Clearly the presence of foreign DNA alone is not enough to determine how we think about a particular organism. In fact, some high profile GMOs that have been in the news lately are cisgenic organisms with no inter-species DNA swaps, such as the non-browning arctic apple.

Kinda creepy
No foreign DNA, but still kinda creepy

Is modifying a trait beyond all recognition through selective breeding equivalent to creating a cisgenic GMO?

No foreign DNA, DEFINITELY not found in nature, kinda creepy.
No foreign DNA, DEFINITELY not found in nature, kinda creepy.

I don’t claim to have any answers, I mostly just want to highlight an interesting result, and emphasize the importance of considering context. The discussion about GMOs all too often devolves into knee-jerk diatribes about what is “natural” or “unnatural.” I’d argue that those adjectives are pretty meaningless. Biology is WAY stranger than fiction: freaky mutants occur with shocking frequency.

Some mutants are freakier than others
Some mutants are freakier than others

I think a more important question to ask is not whether a given technology is “natural” but rather if it is “intentional,” and, if so, what is the intent? An arctic apple and a Shit-Tzu both represent humans monkeying around with another organism’s genome to produce a desirable trait, although on radically different time scales. Clearly, in the case of the cultivated sweet potato, “intention” is out of the picture: the original genetic modification event occurred because some bacteria needed a niche. In this case humans and bacteria collaborated to make a GMO sweet potato: the bacteria contributed the transgenics, the humans provided the power of selection. However, the murky question of why that modified potato appealed to our agricultural ancestors remains unanswered.

God I love sweet potatoes
God I love sweet potatoes

I strongly suspect that we will discover many additional transfers of genes between bacteria and higher organisms as we sequence more genomes. Bacteria have been around for a LONG time. We naked apes might be the loudest and most obvious organisms on planet Earth, but the tiny cells living on us, around us, and inside us have an outsized influence for their small statures.

Dear Bacillus: I love you, I'm sorry I spend so much time messing with your genome.
Dear Bacillus: I love you, I’m sorry I spend so much time messing with your genome.

Have a HAPPY THURSDAY!

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