The genetically engineered potato can be stored in cool temperatures for far longer than standard varieties without sucrose – the compound that stores the sugars in potatoes – converting into reducing sugars such as fructose and glucose. Without as many reducing sugars, off-color browning and caramelization can be minimized, leading to healthier and higher-quality products, including potato chips.
Developed by Michigan State University (MSU) potato breeder Dave Douches, the Kal91.3 was also found to reduce the environmental impact of the growing process as fewer fertilizers and pesticides are needed to maintain it during storage.
“Breeding potatoes is quite challenging because we need so many important traits to line up, but in this case, we just needed one trait to correct the problem,” said Prof Douches, a professor in the Department of Plant Soil and Microbial Sciences and director of the MSU Potato Breeding and Genetics Program.
“Using this biotech strategy, we succeeded in making a potato that was giving us problems into one that’s now commercially valuable.”
The problem with potato storage
Potatoes must be stored at cold temperatures to prevent sprouting and minimize disease, however, the cold triggers an accumulation of reducing sugars. When then subjected to high-temperature processing, these sugars produce dark-colored, bitter-tasting products, along with elevated amounts of acrylamide, a neurotoxin and potential carcinogen.
A 2010 study by a group of US researchers worked out how to silence the gene that produces vacuolar invertase (VI), an enzyme that reacts to external factors like temperatures. Suppressing the gene resulted in less sugar accumulation in cold-stored tubers, as well as a 15-fold acrylamide reduction. The discovery paved the way for Prof Douches and his team to find a way to correct the sugar imbalance that can occur in some of Michigan’s commercial potatoes.
“I’ve always felt as the potato breeder at MSU that using biotechnology as a tool to improve potatoes would be worthwhile,” said Prof Douches.
“I wanted to take this gene and find out whether it could improve a potato that was having a problem with its sugars.”
Multiple experiments between 2014-2015 resulted in a RNA interference (RNAi) construct that silenced VI in an MSU potato variety named Kalkaska. Extensive testing to analyze agronomic characteristics of the Kal91.3 then followed, revealing good shape, size and specific gravity – the measurement of starch content compared to water in the potato.
Historically, chipping potatoes are stored at around 50°F to miminize VI converting sucrose into reducing sugars but doing so has left potatoes more susceptible to storage rot and moisture loss. Kal91.3, however, has shown the ability to be stored at 40°F while maintaining its sugar balance.
“In the Kal91.3 potato, we’re putting the gene in a specific orientation in the DNA that tells the potato the gene won’t work as well as it used to – that is what’s called silencing,” said Prof Douches.
“In Dr Jiang’s approach, he found a way to knock out a segment of the promoter, part of the gene that has information on how the gene itself should work. This leads to the same result as silencing.”
Gene-editing vs genetic-engineering
Further research published earlier this year by the duo details ways of editing that gene.
“His new approach is more of a gene-editing approach, while my current approach is more of genetic-engineering approach,” added Prof Douches.
“There’s a double value to it. The first is that we stabilize the sugars. The invertase silencing slows down the conversion of sucrose into fructose and glucose, so it stabilizes the potato’s sugar while in storage. It’s settling the potato down from a metabolism point of view.
“The second is that we benefit from being able to store the potato for longer periods of time at cooler temperatures.”
The Kal91.3 potato isn’t the first genetically engineered potato with invertase silencing to be exempt from regulation by USDA APHIS. However, it’s the first genetically engineered vegetable developed by a land-grant university to be exempt from regulation.
In January, the US Department of Agriculture’s Animal and Plant Health Inspection Service (USDA APHIS) granted the Kal91.3 potato exemption from the biotechnology regulations placed on GM products after finding it did not to pose an increased plant pest risk compared to its conventionally bred counterpart.
Studies:
Suppression of the vacuolar invertase gene prevents cold-induced sweetening in potato
Authors: Jiming Jiang, Pudota Bhaskar, et al
Plant Physiol. 2010 Oct;154(2):939-48
doi: 10.1104/pp.110.162545.
Auhors: David S Douches, Jiming Jiang, et al
Plant Cell. 2024 May 1;36(5):1985-1999
doi: 10.1093/plcell/koae050.
