Purple tomatoes!

posted in: Food, Science | 11

As I write this, I munch on organic blue corn chips and homemade pico de gallo, made with purple peppers from Small Potatoes Farm (along with heirloom tomatoes and flat leaf Italian parsley and with a glass of local wine from Summerset Winery, yum!). Why choose blue and purple? Anthocyanins, of course. These natural plant compounds are nice to look at, and there is a lot of evidence that they have protecting health qualities for those who eat them, protecting us from diseases like cancer, diabetes, and obesity. So, what do we do to make sure that people can get recommended amounts of anthocyanins?

Anthocyanin-rich berries are delicious but expensive and only available during certain times of year. Most people do not seek out red cabbage or brightly colored heirloom varieties of veggies like carrots and cauliflower. In the US, the most frequently eaten vegetables are potatoes, lettuce, and tomatoes. Purple tomatoes exist, but heirloom tomatoes have issues like splitting and little time till spoilage. This is fine if you buy them at the farmer’s market and eat them the next day, but is not suitable for things like pasta sauce production (cans and bottles are where most people get their RDA of tomatoes, but it turns out they are healthier that way!). Varieties like Cherokee purple, while awesome, don’t produce anthocyanins throughout the fruit.

One option would be to develop tomatoes with high concentrations of anthocyanins. The trait could be bred into varieties that have more of the characteristics needed for processing into pastes and such (although I’m personally looking forward to purple cherry tomatoes, as in the photo). A collaboration of researchers in Europe has done it.

Could this GMO be accepted by people looking for healthier foods? It’s possible, but likely depends on marketing. Some people are simply afraid of anything new, from purple cauliflower (a heirloom variety) to Grapples (infused with grape juice in a dissapointingly boring way). Ah well. For the rest of us, though, purple tomatoes could be an interesting addition to our diets.

As Cathie Martin, the lead researcher, said: this is “certainly the first example of a GMO with a trait that really offers a potential benefit for all consumers.” The health benefits need to be verified in humans, but results look good so far. “In a pilot test, the lifespan of cancer-susceptible mice was significantly extended when their diet was supplemented with the purple tomatoes compared to supplementation with normal red tomatoes (SD).”

Will people be more willing to look into what GM really means when it has potential to benefit them directly? Will they even care how the tomatoes were made if benefits can be shown? This particular GMO transcends a lot of the issues associated with ones currently on the market.

Labeling isn’t as much of an issue when the trait is obvious, and these tomatoes will likely be proudly labeled due to their health benefits. Gene flow isn’t an issue because pollen spread in tomatoes doesn’t seem to be a problem, the trait can be eliminated from fields by sight, and will be of no advantage to wild relatives. The trait could be used with equal benefit in any farming strategy, organic or conventional, large or small, and will have no effect on natural ecosystems (except maybe preventing cancer in herbivores). The only issue left (please remind me if I’ve left any out!) is seed cost due to licensing. However, we must consider that all seed has a cost (simply Google purple tomato seeds to find prices – up to $4 for 20 seeds!), especially for hybrids.

I have to admit to surprise that this research was done in Europe – a collaboration of scientists from the UK, Italy, Germany, and the Netherlands. I’m happy that the research was able to bear fruit before anyone burnt down their lab.

Ok, back to the science.

First, the paper was really easy to read. I think a layperson wouldn’t have too hard of a time reading most it, given a glossary of genetics jargon. Of course, I could be totally wrong on that. Let me know what you think!

The results were achieved by expressing two interacting transcription factors from snapdragons (one of my favorite flowers) that in turn affect expression levels of genes in the anthocyanin pathway. I have to wonder why they ended up using snapdragon genes. You’d think there would be similar transcription factors in tomatoes.

The authors did thoroughly document an entire list of unsuccessful attempts at improving anthocyanins in tomatoes, both by themselves and other labs, including altering expression levels of transcription factors in related pathways and traditional breeding with wild tomatoes, so it seems unlikely that they would overlook a traditional breeding or cisgenic approach in favor of genetic engineering, if the other methods would accomplish their goals.

Although, they did use a cauliflower mosaic virus terminator (stop signal – has nothing to do with the so-called “terminator gene”).  They used a fruit specific promoter, so why not just use the terminator from that gene?

I am very glad that they chose a fruit specific promoter, though. There is no reason to tax the plant’s resources by producing anthocyanins in the leaves and other non-edible parts, unless there is some advantage to expressing them in these parts, such as pest deterrence.

I’m not convinced that they couldn’t do achieve this result with an entirely cisgenic gene construct, but I’m  a particularly big fan of cisgenics. All in all, this seems like a beautiful use of genetic engineering to achieve a result that is important to consumers that could theoretically be achieved by decades of breeding (although it hasn’t yet!). I hope people are able to look past the scary GMO label.

Eugenio Butelli, Lucilla Titta, Marco Giorgio, Hans-Peter Mock, Andrea Matros, Silke Peterek, Elio G W M Schijlen, Robert D Hall, Arnaud G Bovy, Jie Luo, Cathie Martin (2008). Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors Nature Biotechnology DOI: 10.1038/nbt.1506

Follow Anastasia Bodnar:
Anastasia is Policy Director of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favorite produce is artichokes!