1. Abstract

The International Diabetes Federation indicates that in the Western Pacific region, 1 in 8 adults has diabetes. China alone accounts for one-quarter of the world's diabetic population. Diabetes is a chronic disease, and while treatments and medications are available, there is insufficient focus on prevention and everyday dietary management, which is one of the most fundamental methods of self-control. To address this issue, we have engineered sweet potatoes, one of the most starch-rich root crops in the world, known for their high yield and strong adaptability. Additionally, their low retrogradation properties contribute to a superior texture compared to other high-amylose crops. Crops with higher amylose content are excellent sources of resistant starch, which has been shown to lower diabetes risk and promote overall health.

Our goal is to use gene-editing technology to knock out the gene responsible for synthesizing amylopectin in sweet potatoes, thereby increasing the amylose content. Initially, the objective of our project was to develop a meal replacement product that could completely substitute for regular meals, providing an easier means of dietary control for individuals. However, based on our findings through Human Practices, we revised our aim to focus on the development of a low-cost, easy-to-consume, unprocessed sweet potato product, as well as anti-glycemic snacks and desserts specifically targeted at people with diabetes.

Thus, these high-amylose sweet potatoes will be incorporated into affordable products such as sweet potato flour, biscuits, and cakes to reduce postprandial blood glucose fluctuations, supporting both diabetes prevention and the dietary needs of those affected by the condition.

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2. Issue

2.1 Diabetes

Diabetes is a long-term health condition that occurs when the pancreas either fails to produce adequate insulin or when the body cannot use the insulin it produces efficiently [1]. Insulin is a crucial hormone responsible for regulating blood sugar levels. Hyperglycemia, which refers to elevated blood glucose levels, is a common consequence of unmanaged diabetes and can cause significant damage to various bodily systems over time, particularly the nerves and blood vessels [2].

According to the World Health Organization, diabetes and kidney disease caused by diabetes caused an estimated 2 million deaths in 2019; the number of patients rose from 108 million in 1980 to 422 million in 2014 [1]. The condition of diabetes is insidious in its early stages and progresses slowly, but its consequences are very serious, being the leading cause of blindness, kidney failure, heart attack, stroke, and lower limb amputation [1].

2.2 Problems with Current Diabetes Treatment

Current diabetes treatment mainly relies on exogenous insulin injections to reduce blood glucose levels. However, prolonged medication use can result in side effects such as weight gain and hypoglycemia, increase patient dependency on medication, create economic burdens, and lead to psychological stress. Over time, patients may also develop resistance to certain antidiabetic drugs, necessitating higher doses or alternative medications [3].

In a conversation with Dr. Yin from the First Hospital of Qinhuangdao, we learned that diabetes management is often described as a "five-horse carriage," which includes dietary control, physical exercise, medication, diabetes education, and patient self-monitoring of blood glucose levels. Among these, dietary control serves as the cornerstone of management, being essential regardless of the severity [4]. However, it is challenging for diabetic patients to consume anti-glycemic foods at every meal. Firstly, the cost of such foods is often prohibitive, making them difficult to sustain as a regular part of the daily diet. Secondly, many anti-glycemic foods have poor palatability, which further reduces their acceptability and long-term adherence.

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3. Project

3.1 Amylose and Resistant Starch: Characteristics and Health Benefits

Amylose is one of the two main components of starch, the other being amylopectin. Due to its relatively linear structure, amylose molecules are long and tightly packed, forming crystalline regions within the starch granules [5]. These regions are more resistant to enzymatic digestion, making amylose a significant source of resistant starch [5].

Both resistant starch and amylose are converted into glucose at a relatively slow rate in the digestive tract. As a result, compared to foods high in rapidly digestible starches or sugars, they produce a slower glycemic response, thereby effectively lowering the glycemic index (GI). This property is particularly beneficial for individuals with diabetes and those needing to manage blood sugar levels. Furthermore, due to their ability to increase the viscosity of foods, amylose and resistant starch can slow gastric emptying and prolong satiety, which helps to reduce overall food intake. Additionally, their fermentation in the colon produces short-chain fatty acids, which contribute to enhanced gut health [6].

3.2 Advantages of High-Amylose Derived from Sweet Potato (Ipomoea batatas)

Currently, the common sweet potato (Ipomoea batatas) predominantly contains two types of starch: amylose and amylopectin. Generally, sweet potato starch is primarily composed of amylopectin, with a relatively low content of amylose. The amylose content in common sweet potatoes is typically around 20%, while amylopectin makes up approximately 80% [7]. In the market, sweet potatoes are widely used as a raw material for staple foods and starch products. In many regions, people use sweet potatoes as an alternative to staples like rice and noodles. Additionally, sweet potatoes are often processed into various food products, such as sweet potato flour, chips, and cakes, which are popular among consumers.

High-amylose starch is derived from various sources, including high-amylose maize starch, high-amylose sweet potato starch, high-amylose wheat starch, high-amylose rice starch, high-amylose pea starch, and high-amylose potato starch. Among these, high-amylose sweet potato starch has several distinct advantages: it contains a higher proportion of resistant starch, offers a softer texture, and has a naturally sweet flavor [5]. These attributes can help reduce the aversion that diabetic patients may have towards typical anti-diabetic foods that are often perceived as unpalatable. Moreover, compared to starches from other sources such as corn or wheat, sweet potato starch is richer in natural vitamins (such as vitamins A and C) and minerals (such as potassium, calcium, and iron), providing greater nutritional value [8].

Additionally, sweet potatoes are characterized by their high yield, diverse range of downstream products, wide adaptability, resistance to environmental stress, tolerance to poor cultivation and management practices, low fertilizer and water requirements, minimal pest and disease damage, and the need for little or no pesticide application [9].

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3.3 What Do We Do? - Increase the Biosynthesis of Amylose in Sweet Potato

Amylose is a linear polymer consisting mainly of α-D-1,4 glucan chains, whereas amylopectin is a highly branched glucan with α-1,6 glycosidic bonds [10]. In plants, starch biosynthesis is a complex process that requires the synergistic action of various enzymes, including granule-bound starch synthase (GBSS), ADP-glucose pyrophosphorylase (ADPG), starch synthase (SS), starch branching enzymes (SBE) and starch debranching enzyme (DBE) [11]. Amylose is mainly synthesized by GBSS, while amylopectin is synthesized by the synergistic action of SS, SBE and DBE. During starch biosynthesis, SBE catalyzes the amylopectin α-1,6-glycosidic bond and participates in the formation of short chains within the amylopectin clusters, thus SBE plays an important role in the formation of amylopectin [11,12].

Therefore, increasing the content of amylose in crops can be achieved by two ways: overexpression of the GBSS gene to promote amylose synthesis, and inhibition of the expression of amylopectin synthesis genes, such as SBE, to reduce the content of amylopectin and promote amylose synthesis. Recent studies have demonstrated that the knockout of the SBEII gene in sweet potatoes (SBE genes consist of two homologous genes, SBEI and SBEII) leads to a significant increase in the proportion of amylose compared to the wild type [12].

Based on the advantages of sweet potato, we plan to use the gene editing technology CRISPR/Cas9 to knock out both SBEI and SBEII in sweet potato to further increase the content of amylose in it. The genome editing technology CRISPR/Cas9 enables precise modification of DNA sequences in vivo and is efficient enough to offer the possibility of crop improvement [13,14].

Initially, the objective of our project was to develop a meal replacement product that could completely substitute for regular meals, providing an easier means of dietary control for individuals. However, based on our findings through Human Practices, we recognized that cost could be a major barrier to the widespread adoption of anti-glycemic foods. Therefore, we revised our aim to focus on the development of a low-cost, easy-to-consume, unprocessed sweet potato product, as well as anti-glycemic snacks and desserts specifically targeted at people with diabetes.

These high-amylose sweet potatoes will be incorporated into affordable products such as sweet potato flour, biscuits, and cakes to reduce postprandial blood glucose fluctuations, supporting both diabetes prevention and the dietary needs of those affected by the condition.

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References

  1. World Health Organization. Diabetes Fact Sheet.
  2. Deutsch AJ, Ahlqvist E, Udler MS. Phenotypic and genetic classification of diabetes. Diabetologia. 2022 Nov;65(11):1758-1769.
  3. Ziegler R, Neu A. Diabetes in Childhood and Adolescence. Dtsch Arztebl Int. 2018 Mar 2;115(9):146-156.
  4. Basiak-Rasała A, Różańska D, Zatońska K. Food groups in dietary prevention of type 2 diabetes. Rocz Panstw Zakl Hig. 2019;70(4):347-357.
  5. Zhong Y, Tai L, Blennow A, Ding L, Herburger K, Qu J, Xin A, Guo D, Hebelstrup KH, Liu X. High-amylose starch: Structure, functionality and applications. Crit Rev Food Sci Nutr. 2023;63(27):8568-8590.
  6. Wang S, De Paepe K, Van de Wiele T, Fu X, Wang S, Zhang B, Huang Q. Starch-entrapped microspheres enhance gut microbiome-mediated anti-obesity effects of resistant starch in high-fat diet induced obese C57BL/6J mice. Food Res Int. 2023 Oct;172:113215.
  7. Guo K, Liu T, Xu A, Zhang L, Bian X, Wei C. Structural and functional properties of starches from root tubers of white, yellow, and purple sweet potatoes. Food Hydrocolloids. 2019;89:829-836.
  8. Zheng Y, Wang Q, Li B, Lin L, Tundis R, Loizzo MR, Zheng B, Xiao J. Characterization and Prebiotic Effect of the Resistant Starch from Purple Sweet Potato. Molecules. 2016 Jul 19;21(7):932.
  9. Wang X, Li Q, Cao Q, Ma D. Current Status and Future Prospective of Sweet potato Production and Seed Industry in China. Scientia Agricultura Sinica. 2021;54(3):483-492.
  10. Ma XH, Zhang WL, Zhang MJ. Research status of corn starch. Cereals & Oils. 2019;32(2):4−6. (in Chinese)
  11. Wu M, Huang J, Shi TX, et al. CRISPR/Cas9 Technology-generated High-amylose Rice Varieties. Fujian Journal of Agricultural Sciences. 2024;39(1):17−24.
  12. Wang H, Wu Y, Zhang Y, Yang J, Fan W, Zhang H, Zhao S, Yuan L, Zhang P. CRISPR/Cas9-Based Mutagenesis of Starch Biosynthetic Genes in Sweet Potato (Ipomoea Batatas) for the Improvement of Starch Quality. Int J Mol Sci. 2019 Sep 23;20(19):4702.
  13. Liu YG, Li GS, Zhang YL, et al. Current advances on CRISPR/Cas genome editing technologies in plants. Journal of South China Agricultural University. 2019;40(5):38−49. (in Chinese)
  14. Wang H, Wu Y, Zhang Y, Yang J, Fan W, Zhang H, Zhao S, Yuan L, Zhang P. CRISPR/Cas9-Based Mutagenesis of Starch Biosynthetic Genes in Sweet Potato (Ipomoea Batatas) for the Improvement of Starch Quality. Int J Mol Sci. 2019 Sep 23;20(19):4702.