Texas A&M AgriLife researchers are looking to learn how to change the ratio of the two starch molecules found in potatoes – amylose and amylopectin – to increase culinary and industrial applications.
Waxy potatoes, for example, have applications in the bioplastics production lines, food additives, adhesives, and alcohol due to their high amylopectin content.
Two articles published recently in the International Journal of Molecular Sciences and Plant Cell, Tissue, and Organ Culture describe how CRISPR/Cas9 technology can advance the use of the world’s largest vegetable crop.
CRISPR/Cas9 technology has expanded breeders’ toolkit, and it represents a more direct, faster way to incorporate desired traits into popular commercial potato crop varieties.
In the first study, highlighted in the Plant Cell, Tissue and Organ Culture article, a potato line containing four copies of gfp, a jellyfish gene that allows a fluorescence-based visualization of the gene’s activity, was targeted for mutation using the CRISPR/Cas9 system. In essence, this project provided an easy-to-see trait that enabled researchers to optimize the methodology.
Among the various potato cultivars evaluated in the first study, the Yukon Gold strain regenerated the best, and so it was used for the second study. In the second knockout study, described in the International Journal of Molecular Sciences, the native gene gbss in the tetraploid Yukon Gold strain was targeted to effectively eliminate amylose. The result was a potato with starch-rich in amylopectin and low in amylose.
“The information and knowledge we gained from these two studies will help us introduce other desirable traits in this very important crop,” Keerti Rathore, Ph.D., AgriLife Research plant biotechnologist in the Texas A&M Institute for Plant Genomics and Biotechnology and Department of Soil and Crop Sciences, said, cited by Eurekalert.
Isabel Vales, Ph.D., an AgriLife Research potato breeder in the Texas A&M Department of Horticultural Sciences, noted that potatoes with low to medium starch levels are frequently used for fresh or table stock. Additional important considerations for the fresh market include tuber appearance, which includes skin texture, skin color, flesh color, and tuber shape. Specialty potato varieties with different shapes, such as fingerlings, smaller sizes, and red, purple, or yellow skin and flesh colors, have recently gained popularity due to their ease of cooking and increased nutritional value.
“Potato tuber shape is less important for industrial purposes than it is for human consumption. Potato tubers with external deformities caused by heat or drought stress or other factors can be re-directed to myriad uses, including food for dogs and cattle. In addition, potato starch can produce ethanol for fuel or in beverages like vodka; a biodegradable substitute for plastics; adhesives, binders, texture agents, and fillers for the pharmaceutical, textile, wood, and paper industries, and other sectors. For industrial applications, the amount and type of starch in a potato are important considerations,” Vales mentioned.
Starches Higher in Amylopectin are Desirable for Processed Food
Stephany Toinga, Ph.D., a Texas A&M AgriLife Research postdoctoral associate with Vales, said that starches higher in amylopectin are desirable for processed food and other industrial applications due to their unique functional properties. Such starches, for example, are preferred for use as a stabilizer and thickener in food products, as well as an emulsifier in salad dressings. Amylopectin starch is used in frozen foods due to its freeze-thaw stability. Furthermore, potatoes high in amylopectin starch produce more ethanol than those high in other starches.
According to the experts mentioned above, developing potato cultivars with modified starch could open up new possibilities. Potatoes with high amylopectin to amylose ratio, such as the gene-edited Yukon Gold strain, have industrial applications in addition to traditional uses. Potatoes with high amylose levels and low amylopectin levels, on the other hand, would be preferred for human consumption.
Amylose acts like fiber and does not release glucose as easily as amylopectin, resulting in a lower glycemic index and making potatoes more acceptable to diabetics.
The T2-7 tuber starch could find industrial applications in the paper and textile sectors such as adhesives/binders, bioplastics, and ethanol industries. Tuber starch from this experimental strain, because of its freeze-thaw stability without the need for chemical modifications, should also be useful in producing frozen foods. Potatoes with amylopectin as the exclusive form of starch should also yield more ethanol for industrial use or to create alcoholic beverages.
As the next step for these studies, the T2-7 strain has been self-pollinated and crossed with the Yukon Gold strain donor and other potato clones to eliminate the transgenic elements.
