Modest potatoes are a rich source of not only dietary carbohydrates for humans, but also starch for many industrial applications. Texas A&M AgriLife scientists are learning how to change the ratio of two potato starch molecules - amylose and amylopectin - to increase both culinary and industrial applications.
For example, wax potatoes, which have a high content of amylopectin, are used in the production of bioplastics, food additives, glues and alcohol.
Two articles recently published in International Journal of Molecular Sciences and the Culture of plant cells, tissues and organs journals describe how CRISPR technology can improve the use of the world’s largest vegetable crop.
Both papers include the work of Dr. Stephani Toing, a graduate student in the laboratory of Dr. Keerty Rathore, a plant biotechnologist at AgriLife Research at the Texas A&M Institute of Plant Genomics and Biotechnology and the Department of Soil and Crop Science. Also co-author of both papers was Isabel Wales, Ph.D., potato grower AgriLife Research in the Texas Department of Horticultural Sciences. Toinga is now a postdoctoral fellow at Texas A&M AgriLife Research with Wales.
“The information and knowledge we gained from these two studies will help us introduce other desirable traits of this very important crop,” Rathor said.
Facts about potatoes
Potato is the number one vegetable crop in the world and the third most important crop for human consumption, only behind rice and wheat in global production. Potatoes are grown in over 160 countries on 40.8 million hectares and serve as staple food for more than a billion people.
With medium-sized potatoes providing about 160 calories, mostly derived from starch, tubers are an important source of energy for many people around the world, Rathore said. Potatoes also provide other essential nutrients, including vitamins and minerals.
Potato is a crop in the cold season that is relatively sensitive to heat and drought stress. The crop also suffers from pests such as Colorado potato beetle, aphids and nematodes, as well as diseases including early and late blight, zebrafish, dry rot Fusarium and numerous viral diseases. The late stain was the cause of the Irish potato hunger.
Starch is crucial for both dietary and industrial use
The amount of starch in potato tubers is the main factor that determines the use of potatoes. Potatoes with a high starch content are often used to make processed foods such as french fries, chips and dehydrated potatoes, Vales said.
Potatoes with low to medium levels of starch are often used for the fresh or table market, she said. For the fresh market, additional important considerations are the appearance of the tubers, including skin texture, skin color, flesh color, and tuber shape. Recently, there have been special types of potatoes of various shapes, such as fingerlings; smaller size; and red, purple, or yellow skin and flesh colors are becoming popular because of their convenience in cooking and increased nutritional value.
The shape of potato tubers is less important for industrial purposes than for human consumption, Vales said. Potato tubers with external deformities caused by heat stress or drought or other factors can be diverted to countless uses, including dog and cattle food. In addition, potato starch can produce ethanol for fuel or in beverages such as vodka; biodegradable substitute for plastic; or adhesives, binders, textures and fillers for the pharmaceutical, textile, wood and paper industries and other sectors.
For industrial applications, the amount and type of starch in potatoes are important considerations.
Toinga said that starches with a high content of amylopectin are desirable for processed foods and other industrial applications because of their unique functional properties. For example, such starches are a preferred form for use as a stabilizer and thickener in food products and as an emulsifier in salad dressings. Due to its stability against freezing and thawing, amylopectin starch is used in frozen foods. In addition, potatoes rich in amylopectin starch give higher levels of ethanol compared to those with other starches.
Advantages of growing potatoes with selected starch
Developing varieties of potatoes with modified starch could open new possibilities, Toinga said. Potatoes with high amylopectin and low amylose, such as the genetically engineered Yukon Gold strain described in the International Journal of Molecular Sciences, have industrial applications beyond traditional use.
In contrast, potatoes with high levels of amylose and low levels of amylopectin would be desirable for human consumption, Vales said. Amylose acts like fiber and does not release glucose as easily as amylopectin, which leads to a lower glycemic index and makes potatoes more acceptable for people with diabetes.
CRISPR / Cas9 creates new options
CRISPR / Cas9 technology has expanded the set of tools available to growers, Vales said, and is a more direct, faster means of incorporating desired traits into popular commercial crop varieties. Conventional cultivation is a long-term process that can take 10-15 years.
In addition, she said, due to the complex nature of the potato genome, creating new varieties with the right complement of desirable traits is a challenge for conventional cultivation. Molecular breeding has improved breeding efficiency, and gene editing using CRISPR / Cas9 technology adds another level of sophistication.
“We used the Agrobacterium method to deliver CRISPR reagents to potatoes because it is reliable, efficient and the cheapest compared to all other delivery methods,” Rathore said.
In the first study, highlighted in Culture of plant cells, tissues and organs In the article, the potato line, which contains four copies of gfp, a jellyfish gene that allows visualization of fluorescence-based gene activity, was targeted for mutation using the CRISPR / Cas9 system, Toinga said.
In essence, this project provided an easily noticeable feature that allowed researchers to optimize the methodology.
“Loss of characteristic green fluorescence and gfp gene sequencing after CRISPR treatment indicates that all four copies of the gfp gene may be disrupted, confirming that it should be possible to mutate all four alleles of the native gene in the tetraploid. potatoes, ”Rathore said.
Improved variety Yukon Gold
Among the different potato varieties evaluated in the first study, the Yukon Gold strain regenerated the best, so it was used for the second study. In another knockout study, described in International Journal of Molecular Sciences, the native gbss gene in the tetraploid strain Yukon Gold was targeted to effectively eliminate amylose. The result was potatoes with starch rich in amylopectin and low in amylose.
“One of the knockout events, T2-7, showed normal growth and yield characteristics, but was completely devoid of amylose,” Toinga said.
This tuber starch, T2-7, could find industrial applications in the paper and textile industries such as adhesives / binders, bioplastics and the ethanol industry. Tuberous starch from this experimental strain, due to its stability of freezing and thawing without the need for chemical modifications, should also be useful in the production of frozen food. Potatoes with amylopectin as the exclusive form of starch should also provide more ethanol for industrial use or for the production of alcoholic beverages.
As a next step for these studies, strain T2-7 was self-pollinated and crossed with donor Yukon Gold strain and other potato clones to eliminate transgenic elements.