The potato is not only a source of dietary carbohydrate for humans, but also a source of starch for numerous industrial applications. A&M AgriLife Texas scientists are studying how to change the ratio of two starch molecules in potatoes - amylose and amylopectin - to increase the crop's culinary and industrial uses.
For example, waxy potatoes with a high amylopectin content are used in the production of bioplastics, food additives, adhesives, and alcohol.
Two papers recently published in the International Journal of Molecular Sciences and Plant Cell, Tissue and Organ Culture explore how CRISPR technology can improve potato utilization.
Both papers include work done by Stephanie Toinga, Ph.D., who was a graduate student in the laboratory of Kirti Rathor, Ph.D., AgriLife Plant Biotechnologist at the Texas A&M Plant Genomics and Biotechnology Institute and the Department of Soils. Also co-authoring both papers was Isabelle Weils, Ph.D., potato breeder at AgriLife Research at the Texas A&M Department of Horticultural Science.
“The information and knowledge we have gained from these two studies will help us introduce other desirable traits into this very important crop,” Rathor said.
Potato Facts
The potato is grown in over 160 countries on 40,8 million acres and is the staple food for over a billion people.
A medium-sized potato contains about 160 calories, mostly derived from starch, Rathor says, which is why the tubers are an important source of energy for many people around the world. Potatoes also contain other essential nutrients, including vitamins and minerals.
Starch is of key importance for both dietary and industrial uses.
The amount of starch in potato tubers is the main factor in determining the use of potatoes.
High-starch potatoes are often used to make processed foods like french fries, chips and dried potatoes, Wales says.
Low- and medium-starch potatoes are often used fresh or as table potatoes, she says. For fresh consumption of tubers, additional important factors are the appearance of the tuber, including skin texture, skin color, flesh color, and tuber shape. Recently, special varieties of potatoes of various shapes have appeared, such as baby; with red, purple or yellow skin and flesh are becoming popular because of their ease of preparation and increased nutritional value.
In addition, ethanol can be produced from potato starch for fuel or alcoholic beverages; biodegradable plastic substitute; or adhesives, binders, texturizing agents and fillers for the pharmaceutical, textile, wood and paper industries and other sectors of the economy.
For industrial applications, it is important to consider the amount and type of starch in potatoes.
Toinga believes that high amylopectin starches are desirable for food and other industrial uses due to their unique functional properties. For example, such starches are the preferred form for use as a stabilizer and thickener in foods and as an emulsifier in salad dressings. Because of its freeze-thaw stability, amylopectin starch is used in frozen foods. In addition, potatoes rich in amylopectin starch produce higher levels of ethanol compared to potatoes with other starches.
Benefits of Potato Breeding with Selected Starch
Toinga says developing starch-modified potato varieties could open up new possibilities. Potatoes that are high in amylopectin and low in amylose, such as the gene-edited Yukon Gold she described in the International Journal of Molecular Sciences, have industrial uses beyond their traditional uses.
In contrast, potatoes with high amylose levels and low amylopectin would be desirable for human consumption, Wales said. Amylose acts like fiber and does not release glucose as easily as amylopectin, resulting in a lower glycemic index and making potatoes more palatable for people with diabetes.
CRISPR/Cas9 creates new opportunities
CRISPR/Cas9 technology has expanded the toolbox available to breeders and provides a more direct and faster means of incorporating desired traits into popular commercial crop varieties, Weils notes. Traditional breeding is a long process that can take 10-15 years.
In addition, due to the complex nature of the potato genome, creating new varieties with the right set of desirable traits is a challenge for conventional breeding, she says. Molecular technologies have increased the efficiency of selection, and gene editing using CRISPR/Cas9 technology adds another layer of complexity.
Improved variety Yukon Gold
Among the various potato varieties evaluated in the first study, Yukon Gold regenerated the best, so it was used in the second study. The result was a potato with a high content of amylopectin and a low content of amylose in starch.
“One of the knocked-out plants, T2-7, showed normal growth and yield characteristics but was completely devoid of amylose,” Toinga said.
Tuber starch, T2-7, has industrial applications in the paper and textile industries as an adhesive/binder, bioplastic, and ethanol production. The tuber starch of this experimental sample, due to its resistance to freezing and thawing without the need for chemical modifications, should also be useful in the production of frozen foods. Potatoes with amylopectin as the only form of starch should also yield more ethanol for industrial use or to create alcoholic beverages.
As a next step in these studies, accession T2-7 was self-pollinated and crossed with a donor strain of Yukon Gold and other potato clones to eliminate transgenic elements.