**Author details**

Manuel Andrés Muñoz\*, Julio César Kalazich, Carolina Verónica Folch, Sandra Valeska Orena and Annelore Winkler

\*Address all correspondence to: manuel.munozd@inia.cl

Institute of Agricultural Research INIA, Regional Center Remehue, Chile

#### **References**


[6] Muñoz M, Folch C, Rodriguez F, Kalazich J, Orena S, Santos J, Vargas R, Fahrenkrog A, Puga A. Genotype number and allelic diversity overview in the national collection of Chilean potatoes. Potato Research. 2016;**59**(3):227-240

[17] Rietman H. Putting the *Phytophthora infestans* genome sequence at work; identification of many new *R* and *Avr* genes in *Solanum* [PhD thesis]. Wageningen University; 2011 [18] Darrasse A, Priou S, Kotoujansky A, Bertheau Y. PCR and restriction fragment length polymorphism of a pel gene as a tool to identify *Erwinia carotovora* in relation to potato

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[19] Du Z, Chen J, Hiruki C. Optimization and application of a multiplex RT-PCR system for simultaneous detection of five potato viruses using 18S rRNA as an internal control.

[20] Termorshuizen AJ. Fungal and fungus-like pathogen of potato. In: Vreugdenhil D, editor. Potato Biology and Biotechnology. Advances and Perspectives. Oxford, UK: Elsevier;

[21] Mayton H, Rauscher G, Simko I, Fry W. Evaluation of the *Rpi-ber* late blight resistance gene for tuber resistance in the field and laboratory. Plant Breeding. 2011;**130**:464-468 [22] Rodewald J, Trognitz B. Solanum resistance genes against *Phytophthora infestans* and their corresponding avirulence genes. Molecular Plant Pathology. 2013;**14**:740-757. DOI:

[23] Tiwari J, Siddappa S, Singh B, Kaushik S, Chakrabarti S, Bhardwaj V, Chandel P. Molecular markers for late blight resistance breeding of potato: An update. Plant

[24] Mastenbroek C. Investigations into the inheritance of the immunity from *Phytophthora* 

[25] Jo KR. Unveiling and deploying durability of late blight resistance in potato. From natural stacking to cisgenic stacking [PhD Thesis]. Netherlands: Wageningen University;

[26] Ordonez ME, Forbes GA, Trognitz BR. Resistance to late blight in potato. A putative gene that suppresses R genes and is elicited by specific isolates. Euphytica. 1997;**95**:167-172

[27] Jo KR, Kim CK, Kim SJ, Kim TY, Bergervoet M, Jongsma M, Visser R, Jacobsen E, Vossen J. Development of late blight resistant potatoes by cisgene stacking. BMC Biotechnology.

[28] Amin M, Mulugeta N, Thangavel S. Field evaluation of new fungicide, Victory 72 WP for management of potato and tomato late blight (*Phytophthora infestans* (Mont) de Bary) in West Shewa Highland, Oromia, Ethiopia. Journal of Plant Pathology and Microbiology.

*infestans* de Bary of *Solanum demissum* Lindl. Euphytica. 1952;**1**:187-198

diseases. Applied and Environmental Microbiology. 1994;**60**(5):1437-1443

Plant Disease. 2006;**90**:185-189

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[17] Rietman H. Putting the *Phytophthora infestans* genome sequence at work; identification of many new *R* and *Avr* genes in *Solanum* [PhD thesis]. Wageningen University; 2011

[6] Muñoz M, Folch C, Rodriguez F, Kalazich J, Orena S, Santos J, Vargas R, Fahrenkrog A, Puga A. Genotype number and allelic diversity overview in the national collection of

[7] Finkers-Tomczak A, Bakker E, de Boer J, van der Vossen E, Achenbach U, Golas T, Suryaningrat S, Smant G, Bakker J, Goverse A. Comparative sequence analysis of the potato cyst nematode resistance locus H1 reveals a major lack of co-linearity between three haplotypes in potato (*Solanum tuberosum* ssp.). Theoretical and Applied Genetics.

[8] Galek R, M, Rurek De Jong, W.S, Pietkiewicz G, Augustyniak H, Sawicka-Sienkiewicz E. Application of DNA markers linked to the potato H1 gene conferring resistance to pathotype Ro1 of *Globodera rostochiensis*. Journal of Applied Genetics. 2011;**52**:407-411 [9] Paal J, Henselewski H, Muth J, Meksem K, Menéndez CM, Salamini F, Ballvora A, Gebhardt C. Molecular cloning of the potato *Gro1-4* gene conferring resistance to pathotype Ro1 of the root cyst nematode Globodera rostochiensis, based on a candidate gene

[10] Jacobs J, van Eck HJ, Horsman K, Arens P, Verkerk-Bakker B, Jacobsen E, Pereira A, Willem Stiekema J. Mapping of resistance to the potato cyst nematode *Globodera rostochiensis* from the wild potato species *Solarium vernei*. Molecular Breeding. 1996;**2**:51-60

[11] Kasai K, Morikawa Y, Sorri VA, Valkonen JPT, Gebhardt C, Watanabe KN. Development of SCAR markers to the PVY resistance gene Ry*adg* based on a common feature of plant

[12] Bendahmane A, Querci M, Kanyuka K, Baulcombe D. *Agrobacterium* transient expression system as a tool for the isolation of disease resistance genes: Application to the Rx2

[13] Bendahmane A, Kanyuka K, Baulcombe D. The *Rx* gene from potato controls separate

[14] Ballvora A, Ercolano MR, Weiû J, Meksem K, Bormann CA, Oberhagemann P, Salamini F, Gebhardt C. The *R1* gene for potato resistance to late blight (*Phytophthora infestans*) belongs to the leucine zipper/NBS/LRR class of plant resistance genes. The Plant Journal.

[15] Kim HJ, Lee HR, Jo KR, Mortazavian SM, Huigen DJ, Evenhuis B, Kessel G, Visser RGF, Jacobsen E, Vossen JH. Broad spectrum late blight resistance in potato differential set plants Ma*R8* and Ma*R9* is conferred by multiple stacked R genes. Theor. Appl. Genet.

[16] Huang S, van der Vossen EAG, Kuang H, Vleeshouwers VGAA, Zhang N, Borm TJA, van Eck HJ, Baker B, Jacobsen E, Visser RGF. Comparative genomics enabled the cloning of the R3a late blight resistance gene in potato. The Plant Journal. 2005;**42**(2):251-261

virus resistance and cell death responses. The Plant Cell. 1999;**11**:781-791

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2002;**30**(3):361-371

2011;**124**:923-935


**Chapter 2**

**Provisional chapter**

**Genetically Modified Potato as a Source of Novel**

**Genetically Modified Potato as a Source of Novel** 

DOI: 10.5772/intechopen.71079

Significant progress has been made in understanding of carbohydrate (starch) biosynthesis through molecular biology and genetic engineering techniques. Genetic modification of plants has a great potential to produce novel carbohydrates with unique properties that cannot be generated by conventional breeding approaches. Starch is the predominant carbohydrate in potatoes and serves as an energy reserve for the plant. Genetic engineering of potato (*Solanum tuberosum* L.) tuber can revolutionise the synthesis of unique starches with altered physical and chemical properties that are engineered to meet the specific industrial requirements. In addition to expression of foreign genes involved in carbohydrate biosynthesis, genes regulating the carbohydrate metabolism, transport and resource partitioning have also been achieved. Here we summarise the recent progress made towards modifications of the biosynthetic pathways by which potato can produce novel carbohydrates. Further, we discuss the prospects of engineering potatoes for pro-

**Keywords:** carbohydrate metabolism, starch, genetic engineering, novel carbohydrates,

The most abundant bio-compounds on our planet are the carbohydrates which is synthesised by green plants during the process of photosynthesis. More than 100 billion metric tons of CO<sup>2</sup>

O per year are converted into carbohydrates during the process of photosynthesis [1]. The carbohydrates converted into the starch in the plant plastids which is the major storage

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

**Carbohydrates**

**Carbohydrates**

Deepak Singh Bagri and

**Abstract**

**1. Introduction**

and H<sup>2</sup>

Deepak Singh Bagri and

Chandrama Prakash Upadhyaya,

Chandrama Prakash Upadhyaya,

http://dx.doi.org/10.5772/intechopen.71079

Additional information is available at the end of the chapter

duction of structural and non-structural carbohydrates.

*Solanum tuberosum* L., sucrose transport

Additional information is available at the end of the chapter

Devanshi Chandel Upadhyaya

Devanshi Chandel Upadhyaya

**Provisional chapter**

## **Genetically Modified Potato as a Source of Novel Carbohydrates Carbohydrates**

**Genetically Modified Potato as a Source of Novel** 

DOI: 10.5772/intechopen.71079

Chandrama Prakash Upadhyaya, Deepak Singh Bagri and Devanshi Chandel Upadhyaya Deepak Singh Bagri and Devanshi Chandel Upadhyaya Additional information is available at the end of the chapter

Chandrama Prakash Upadhyaya,

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71079

#### **Abstract**

Significant progress has been made in understanding of carbohydrate (starch) biosynthesis through molecular biology and genetic engineering techniques. Genetic modification of plants has a great potential to produce novel carbohydrates with unique properties that cannot be generated by conventional breeding approaches. Starch is the predominant carbohydrate in potatoes and serves as an energy reserve for the plant. Genetic engineering of potato (*Solanum tuberosum* L.) tuber can revolutionise the synthesis of unique starches with altered physical and chemical properties that are engineered to meet the specific industrial requirements. In addition to expression of foreign genes involved in carbohydrate biosynthesis, genes regulating the carbohydrate metabolism, transport and resource partitioning have also been achieved. Here we summarise the recent progress made towards modifications of the biosynthetic pathways by which potato can produce novel carbohydrates. Further, we discuss the prospects of engineering potatoes for production of structural and non-structural carbohydrates.

**Keywords:** carbohydrate metabolism, starch, genetic engineering, novel carbohydrates, *Solanum tuberosum* L., sucrose transport

#### **1. Introduction**

The most abundant bio-compounds on our planet are the carbohydrates which is synthesised by green plants during the process of photosynthesis. More than 100 billion metric tons of CO<sup>2</sup> and H<sup>2</sup> O per year are converted into carbohydrates during the process of photosynthesis [1]. The carbohydrates converted into the starch in the plant plastids which is the major storage

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

carbohydrate found in various types of green plant tissues and organs. Two types of starch are reported to be present in the plants which are distinguishable as the 'transitory starch' and the 'storage starch'. The transitory starch is synthesised and accumulated in chloroplasts of green leaves during photosynthesis and degraded throughout the night to provide substrates for respiration and continued sucrose synthesis to supply to sink tissues [2]. The storage starch is synthesised in amyloplasts and typically associated with sink organs, such as stems, seeds, roots, and tubers. This type of starch is accumulated during different developmental stages and utilised during various periods of dormancy, germination, growth, or other specific processes. The storage starch is deposited in granules rich in amylose content than that observed in the transitory starch [3, 4].

Starch which is known as the product of the plant photosynthetic carbohydrates, is commercially isolated from a wide range of sources including cereal grains such as corn, wheat, rice, and sorghum; roots and tubers such as potato, sweet potato, cassava, and arrowroot; and stem and pith such as sago. The composition of naturally occurring starch is universal, irrespective of its source, with the main component as amylopectin (75%) and a minor component as amylose (25%). Amylose and amylopectin are synthesised in the plastids, where they assemble into a semi-crystalline granule. The starch found in potato tuber is distinct granules approximately 10–100 μm in diameter [5]. Compared with other commodity starches, the potato starch granules are relatively larger, smooth with a high content of covalently linked phosphate, long amylopectin chains and high-molecular weight amylose. The granules are synthesised by two polysaccharides consisting exclusively of glucose as the monomer component. The glucopyranosyl residues are connected through α-d-(1,4)-linkages forming chains through α-d-(1,6)-branches at the reducing end side linked to similar other chains. The industrial application of starch includes the manufacture of high-quality paper [6] and generation of viscous hydrocolloid systems to be used for food processing [7]. However, the well-ordered and dense structure of the native potato starch granule renders it resistant to enzymatic degradation by hydrolytic enzymes such as amyloglucosidases and α-amylases [8], which is very important in industrial applications. Amylopectin is the major component of starch in general, and in potato it normally constitutes 70–80% by weight [9] regardless of the size of the granules [10]. Approximately 4–6% of linkages are of the α-d-(1,6)-type, making it extensively branched. The weight-average molecular size of amylopectin is on the order of 107 Da [11, 12]; as a result, the macromolecule consists of a huge number of relatively short chains with an average degree of polymerisation (DP) of 21–28 residues [13, 14]. The amylose is considerably smaller than amylopectin and is basically a linear polymer comprising of 2000–5000 residues [5]. This composition may affect the physicochemical properties, such as gelatinization, texture, moisture retention, viscosity, and product homogeneity that are determinants for its industrial applications. Besides the polysaccharide components, potato starch consists of low amounts of material of a non-carbohydrate nature. Less than 0.5% of the granules are proteins [9], apparently involved in starch synthesis. Potato starch also contains phosphorus in the form of phosphate covalently linked to the amylopectin component. It is

Genetically Modified Potato as a Source of Novel Carbohydrates

http://dx.doi.org/10.5772/intechopen.71079

21

considered an important factor contributing to potato starch properties.

**2. Mechanism underlying starch biosynthesis in potato**

The photosynthesis is the primary metabolic mechanism for the carbohydrate biosynthesis which is well-known phenomenon of the plant that takes place with the help of the chlorophyll and light. However, the conversion of carbohydrates to starch granule is a subtle equilibrium between proficient packing of the glucan chains and the prospect of breaking these structures during degradation. Hence, a series of enzyme catalytic activities are required to complete this process in the starch biosynthesis. These include three steps, the first is the activation of the major carbohydrate, the glucose molecule, second step is the elongation of the glucan chain, and the final step is the transfer of linear backbone chains forming branched structures (**Figure 1**). The activation of the glucose residues to form adenosine diphosphoglucose

According to the recent reports published by the Food and Agricultural Organisation Statistics (FAO statistics), the potato (*Solanum tuberosum* L.) stands at the world's 4th major crop in terms of yield after rice, wheat and corn, and in terms of area under cultivation, its stands at the 8th position. The potato is grown for its tuber which is considered as is a high-energy staple food around the world and high productivity per unit area due to its intense cultivation. Thus, the potato represents one of the best candidates for alleviating food shortages. Potato belongs to *Solanaceae* family, is the perennial herbaceous plant having white to purple flowers with yellow stamens. Some potato cultivar bears small green fruits, each containing up to 300 seeds. Potato is grown from the botanical seeds or usually propagated vegetatively by planting pieces of tubers containing eyes or dormant buds which develop into new shoots (sprouts) when grown under suitable conditions. Potato tubers are rich in starch, storage proteins and develop by the morphological changes of the underground stem into stolon bearing auxiliary buds and scars of scale leaves. The total carbohydrates in potato tuber range from 1.0 to 7.0 g/kg. The reducing sugar (glucose, fructose) concentrations are higher in young tubers and reduced significantly near the end of the cultivating season. Starch is the prime carbohydrate component of the potato dry matter containing the amylose and amylopectin. Starch has conventionally been used in the food industry to augment the functional properties of various foods. The physicochemical and functional properties of starch system vary with the starch biological origin. The structural characteristics and amylose-to-amylopectin ratio of potato starch also vary among cultivars. Nutritional and processing quality of potato products (frozen and dry) are greatly affected by their starch characteristics and content. Several chemical, physical, and enzymatic modifications have been accomplished to improve the processing operation of potato starch. Potato starch can be used in other industrial applications as a gelling agent, thickener, bulking agent, colloidal stabiliser and water-holding agent. However, due to low shear and thermal resistance and high bent towards degradation hinder its use in some industrial food applications. These limitations are generally overcome by starch modification, which can be achieved through derivatization, such as etherification, esterification, cross-linking, and grafting; decomposition (acid or enzymatic hydrolysis and oxidisation); or physical treatment of starch using heat or moisture or pressure, etc. Most of these modifications are usually recognised as non-toxic by the safety authorities. Several modified potato starches with slow digestibility are being developed that may provide nutritional benefits for humans. These starches have the potential to be used for the treatment of certain medical conditions (e.g., glycogen storage disease and *Diabetes mellitus*). The Food and Drug Administration (FDA) controls and emphasises the type and amount of each chemical used in starch modification, as well as the percentage of the substitution.

Starch which is known as the product of the plant photosynthetic carbohydrates, is commercially isolated from a wide range of sources including cereal grains such as corn, wheat, rice, and sorghum; roots and tubers such as potato, sweet potato, cassava, and arrowroot; and stem and pith such as sago. The composition of naturally occurring starch is universal, irrespective of its source, with the main component as amylopectin (75%) and a minor component as amylose (25%). Amylose and amylopectin are synthesised in the plastids, where they assemble into a semi-crystalline granule. The starch found in potato tuber is distinct granules approximately 10–100 μm in diameter [5]. Compared with other commodity starches, the potato starch granules are relatively larger, smooth with a high content of covalently linked phosphate, long amylopectin chains and high-molecular weight amylose. The granules are synthesised by two polysaccharides consisting exclusively of glucose as the monomer component. The glucopyranosyl residues are connected through α-d-(1,4)-linkages forming chains through α-d-(1,6)-branches at the reducing end side linked to similar other chains. The industrial application of starch includes the manufacture of high-quality paper [6] and generation of viscous hydrocolloid systems to be used for food processing [7]. However, the well-ordered and dense structure of the native potato starch granule renders it resistant to enzymatic degradation by hydrolytic enzymes such as amyloglucosidases and α-amylases [8], which is very important in industrial applications. Amylopectin is the major component of starch in general, and in potato it normally constitutes 70–80% by weight [9] regardless of the size of the granules [10]. Approximately 4–6% of linkages are of the α-d-(1,6)-type, making it extensively branched. The weight-average molecular size of amylopectin is on the order of 107 Da [11, 12]; as a result, the macromolecule consists of a huge number of relatively short chains with an average degree of polymerisation (DP) of 21–28 residues [13, 14]. The amylose is considerably smaller than amylopectin and is basically a linear polymer comprising of 2000–5000 residues [5]. This composition may affect the physicochemical properties, such as gelatinization, texture, moisture retention, viscosity, and product homogeneity that are determinants for its industrial applications. Besides the polysaccharide components, potato starch consists of low amounts of material of a non-carbohydrate nature. Less than 0.5% of the granules are proteins [9], apparently involved in starch synthesis. Potato starch also contains phosphorus in the form of phosphate covalently linked to the amylopectin component. It is considered an important factor contributing to potato starch properties.

#### **2. Mechanism underlying starch biosynthesis in potato**

carbohydrate found in various types of green plant tissues and organs. Two types of starch are reported to be present in the plants which are distinguishable as the 'transitory starch' and the 'storage starch'. The transitory starch is synthesised and accumulated in chloroplasts of green leaves during photosynthesis and degraded throughout the night to provide substrates for respiration and continued sucrose synthesis to supply to sink tissues [2]. The storage starch is synthesised in amyloplasts and typically associated with sink organs, such as stems, seeds, roots, and tubers. This type of starch is accumulated during different developmental stages and utilised during various periods of dormancy, germination, growth, or other specific processes. The storage starch is deposited in granules rich in amylose content than that observed in the transitory starch [3, 4].

20 Potato - From Incas to All Over the World

According to the recent reports published by the Food and Agricultural Organisation Statistics (FAO statistics), the potato (*Solanum tuberosum* L.) stands at the world's 4th major crop in terms of yield after rice, wheat and corn, and in terms of area under cultivation, its stands at the 8th position. The potato is grown for its tuber which is considered as is a high-energy staple food around the world and high productivity per unit area due to its intense cultivation. Thus, the potato represents one of the best candidates for alleviating food shortages. Potato belongs to *Solanaceae* family, is the perennial herbaceous plant having white to purple flowers with yellow stamens. Some potato cultivar bears small green fruits, each containing up to 300 seeds. Potato is grown from the botanical seeds or usually propagated vegetatively by planting pieces of tubers containing eyes or dormant buds which develop into new shoots (sprouts) when grown under suitable conditions. Potato tubers are rich in starch, storage proteins and develop by the morphological changes of the underground stem into stolon bearing auxiliary buds and scars of scale leaves. The total carbohydrates in potato tuber range from 1.0 to 7.0 g/kg. The reducing sugar (glucose, fructose) concentrations are higher in young tubers and reduced significantly near the end of the cultivating season. Starch is the prime carbohydrate component of the potato dry matter containing the amylose and amylopectin. Starch has conventionally been used in the food industry to augment the functional properties of various foods. The physicochemical and functional properties of starch system vary with the starch biological origin. The structural characteristics and amylose-to-amylopectin ratio of potato starch also vary among cultivars. Nutritional and processing quality of potato products (frozen and dry) are greatly affected by their starch characteristics and content. Several chemical, physical, and enzymatic modifications have been accomplished to improve the processing operation of potato starch. Potato starch can be used in other industrial applications as a gelling agent, thickener, bulking agent, colloidal stabiliser and water-holding agent. However, due to low shear and thermal resistance and high bent towards degradation hinder its use in some industrial food applications. These limitations are generally overcome by starch modification, which can be achieved through derivatization, such as etherification, esterification, cross-linking, and grafting; decomposition (acid or enzymatic hydrolysis and oxidisation); or physical treatment of starch using heat or moisture or pressure, etc. Most of these modifications are usually recognised as non-toxic by the safety authorities. Several modified potato starches with slow digestibility are being developed that may provide nutritional benefits for humans. These starches have the potential to be used for the treatment of certain medical conditions (e.g., glycogen storage disease and *Diabetes mellitus*). The Food and Drug Administration (FDA) controls and emphasises the type and amount of each chemical

used in starch modification, as well as the percentage of the substitution.

The photosynthesis is the primary metabolic mechanism for the carbohydrate biosynthesis which is well-known phenomenon of the plant that takes place with the help of the chlorophyll and light. However, the conversion of carbohydrates to starch granule is a subtle equilibrium between proficient packing of the glucan chains and the prospect of breaking these structures during degradation. Hence, a series of enzyme catalytic activities are required to complete this process in the starch biosynthesis. These include three steps, the first is the activation of the major carbohydrate, the glucose molecule, second step is the elongation of the glucan chain, and the final step is the transfer of linear backbone chains forming branched structures (**Figure 1**). The activation of the glucose residues to form adenosine diphosphoglucose (ADP-glucose) takes place with the help of enzyme ADP-glucose pyrophosphorylase (AGPase) using the ATP and a molecule of glucose 1-phosphate [15]. This reaction is the rate-limiting step in the starch biosynthesis. In the next step, the elongation of the chain takes place which constitute the amylopectin and finally the starch granule is synthesised with the help of soluble starch synthase (SS) and starch-branching enzymes (SBE). The soluble SS catalyses the elongation of the chain at the non-reducing end in a reaction in which ADP of the ADP-glucose molecule is replaced by the terminal hydroxyl group of the growing glucan chain, creating an elongated linear α-(1,4)-glucan chain. However, only one enzyme is essential recognised as granule bound (GB)-starch synthase (SS) for amylose synthesis. The formation of branched

α-(1,6)-linkages in starch is catalysed by the SBE. In this reaction, an α-(1,4)-linkage within the chain is cleaved and an α-(1,6)-linkage is formed between the reducing end of the cleaved glucan chain and a C-6 linked oxygen of an adjacent chain. The starch-branching enzyme has been reported to exist as multiple enzyme isoforms. The action of debranching activities during biosynthesis seems to be important for correct assembly of the starch granule [16]. This process is generally more complicated as compared to glycogen biosynthesis involving a multitude of different homologous enzymes probably responsible for synthesising specific structures of the starch granule in different tissues and at different developmental stages. Apparently, many of these enzymes interact to form enzyme complexes or metabolomes to channel and direct

Genetically Modified Potato as a Source of Novel Carbohydrates

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23

New cultivars of potato with better yield, disease resistance, have been developed since long time with the help of breeding techniques. Following the advancement of genetic engineering tools, several other potato cultivars with desired yield, dry matter, protein and antioxidant quality, cooking texture (such as waxy, floury), flesh colour, and abiotic stress tolerant plant have also been developed. The demand for starches with special properties useful for industrial food processing has led to the introduction of modified starches using the genetic engineering techniques. Though, there are a lot of information available in the literature on chemical modification of starch, however, genetically modified potato with altered carbohydrates, starch or amylose/amylopectin content, have also been developed. Some of the genetically modified potato starches are being used in the industry under strict control, however, these transgenic varieties of potatoes are not permitted for food use in several countries because of the concerns related to consumer health and the environment. Until these genetically modified potatoes have been given proper clearance by the food authorities and acceptance by the consumers, they may have a good scope for their use in non-food or other industrial applications. We will first describe attempts to alter starch structure to improve starch functionality, then explain how increasing knowledge of the regulation of starch biosynthesis is being used to increase starch production, and finish by summarising new methods for increasing the genetic diversity in crops as well as methods for fine-tuning gene expression in plants in order to bring improved starch-based products with value-added consumer benefits to the marketplace.

**3. Genetic engineering of potato for starch modification**

way to yield high-amylose and high-amylopectin starches.

**3.1. Genetic engineering of potato for starch synthase enzyme**

Starch modification involves efforts to both achieving enhanced starch production and modifies the composition or component structure to impart specific properties to suit final product. The most widely referred target for starch modification is the alteration in the amylose-amylopectin ratio. Several plants have been genetically modified in their starch biosynthetic path-

It is evident that the starch synthase (SS; ADP-glucose:α-1,4 glucosyl transferase) catalyses transfer of the glucosyl moieties from ADP-glucose to the non-reducing end of an α-1,4-glucan [17]. The potato SSs enzymes catalyse the same reaction represented as

substrates and products.

**Figure 1.** Pathway of starch synthesis. ADP-glucose (ADP-Glc), the donor substrate for both amylose and amylopectin, is synthesised by the ADP-Glc pyrophosphorylase (AGPase). The combined action of different starch synthases (SSI, SSII, and SSIII), branching enzymes (BEI and BEII), and the debranching enzyme (DBE) is necessary for the synthesis of amylopectin. Granule-bound starch synthases (GBSSI and GBSSII) use amylopectin as the acceptor substrate to synthesise amylose, which is formed down-stream of amylopectin.

α-(1,6)-linkages in starch is catalysed by the SBE. In this reaction, an α-(1,4)-linkage within the chain is cleaved and an α-(1,6)-linkage is formed between the reducing end of the cleaved glucan chain and a C-6 linked oxygen of an adjacent chain. The starch-branching enzyme has been reported to exist as multiple enzyme isoforms. The action of debranching activities during biosynthesis seems to be important for correct assembly of the starch granule [16]. This process is generally more complicated as compared to glycogen biosynthesis involving a multitude of different homologous enzymes probably responsible for synthesising specific structures of the starch granule in different tissues and at different developmental stages. Apparently, many of these enzymes interact to form enzyme complexes or metabolomes to channel and direct substrates and products.

(ADP-glucose) takes place with the help of enzyme ADP-glucose pyrophosphorylase (AGPase) using the ATP and a molecule of glucose 1-phosphate [15]. This reaction is the rate-limiting step in the starch biosynthesis. In the next step, the elongation of the chain takes place which constitute the amylopectin and finally the starch granule is synthesised with the help of soluble starch synthase (SS) and starch-branching enzymes (SBE). The soluble SS catalyses the elongation of the chain at the non-reducing end in a reaction in which ADP of the ADP-glucose molecule is replaced by the terminal hydroxyl group of the growing glucan chain, creating an elongated linear α-(1,4)-glucan chain. However, only one enzyme is essential recognised as granule bound (GB)-starch synthase (SS) for amylose synthesis. The formation of branched

22 Potato - From Incas to All Over the World

**Figure 1.** Pathway of starch synthesis. ADP-glucose (ADP-Glc), the donor substrate for both amylose and amylopectin, is synthesised by the ADP-Glc pyrophosphorylase (AGPase). The combined action of different starch synthases (SSI, SSII, and SSIII), branching enzymes (BEI and BEII), and the debranching enzyme (DBE) is necessary for the synthesis of amylopectin. Granule-bound starch synthases (GBSSI and GBSSII) use amylopectin as the acceptor substrate to

synthesise amylose, which is formed down-stream of amylopectin.

New cultivars of potato with better yield, disease resistance, have been developed since long time with the help of breeding techniques. Following the advancement of genetic engineering tools, several other potato cultivars with desired yield, dry matter, protein and antioxidant quality, cooking texture (such as waxy, floury), flesh colour, and abiotic stress tolerant plant have also been developed. The demand for starches with special properties useful for industrial food processing has led to the introduction of modified starches using the genetic engineering techniques. Though, there are a lot of information available in the literature on chemical modification of starch, however, genetically modified potato with altered carbohydrates, starch or amylose/amylopectin content, have also been developed. Some of the genetically modified potato starches are being used in the industry under strict control, however, these transgenic varieties of potatoes are not permitted for food use in several countries because of the concerns related to consumer health and the environment. Until these genetically modified potatoes have been given proper clearance by the food authorities and acceptance by the consumers, they may have a good scope for their use in non-food or other industrial applications. We will first describe attempts to alter starch structure to improve starch functionality, then explain how increasing knowledge of the regulation of starch biosynthesis is being used to increase starch production, and finish by summarising new methods for increasing the genetic diversity in crops as well as methods for fine-tuning gene expression in plants in order to bring improved starch-based products with value-added consumer benefits to the marketplace.
