Molecular Plant Breeding 2024, Vol.15, No.2, 63-69 http://genbreedpublisher.com/index.php/mpb 63 Invited Review Open Access Starch Biosynthesis and Engineering Starch Yield and Properties in Cassava Youzhi Li State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Guangxi Research Center for Microbial and Enzyme Engineering Technology, College of Life Science and Technology, Guangxi University, Nanning, 530004, Guangxi, China Corresponding email: dyz@gxu.edu.cn Molecular Plant Breeding, 2024, Vol.15, No.2 doi: 10.5376/mpb.2024.15.0008 Received: 30 Jan., 2024 Accepted: 05 Mar., 2024 Published: 17 Mar., 2024 Copyright © 2024 Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li Y.Z., 2024, Starch biosynthesis and engineering starch yield and properties in cassava, Molecular Plant Breeding, 15(2): 63-69 (doi: 10.5376/mpb.2024.15.0008) Abstract Cassava (Manihot esculenta Crantz), a perennial shrub but a root crop in Euphorbiaceae, produces a bulk of starch in the storage roots and serves as a staple food for millions of people in tropical and subtropical regions. Additionally, cassava starch is widely used in food processing and industrial sectors due to its unique physicochemical properties of swelling and solubility, gelatinization, retrogradation, pasting, and viscoelasticity. Up to now, the starch biosynthesis and improvement have been well reviewed by a large number of literatures at different layers and aspects in other plant species/crops but the understanding is limited in cassava. Therefore, how to increase starch yield and improve starch properties has received great attention. This article briefly reviews plant starch biosynthesis, and complexity of starch biosynthesis, cases of engineering-based improvement of starch yield and properties, quantitative trait loci controlling starch yield and properties, challenges of breeding and engineering, and opportunities and future prospects in cassava. Keywords Cassava (Manihot esculentaCrantz); Starch biosynthesis; Engineering starch; Starch yield; Starch properties 1 Introduction Cassava (Manihot esculenta Crantz) is a perennial shrub but a root crop in Euphorbiaceae. This crop serves as a staple food for millions of people in tropical and subtropical regions because the dry matter in its storage roots contains more than 80% starch (Alves, 2002; El-Sharkawy, 2004). In addition, cassava can grow on barren and drought land where other crops fail due to its stronger tolerance to stressful environments (Alves, 2002). Beyond its role in human nutrition, cassava starch is also a versatile material with a wide range of applications in food processing and industrial sectors (Tappiban et al., 2019) due to its unique physicochemical properties of swelling and solubility, gelatinization, retrogradation, pasting, and viscoelasticity (Chisenga et al., 2019). On these ground, the roles of cassava starch in economic and nutritional value cannot be overstated. Therefore, understanding starch biosynthesis of cassava is very necessary for tailoring it to specific needs. Up to now, a large number of in-depth reviews at different layers and aspects have been conducted on the starch biosynthesis in plants (Martin and Smith, 1995; Hannah and James, 2008; Orzechowski, 2008; Jeon et al., 2010; Kötting et al., 2010; Stitt and Zeeman, 2012; Bahaji et al., 2014; Saripalli and Gupta, 2015; Tappiban et al., 2019; Tetlow and Bertoft, 2020; Huang et al., 2021; Li et al., 2021). But, integrative understanding of cassava starch biosynthesis is relatively limited. Fortunately, the completion of cassava genome sequencing (Wang et al., 2014) provides an excellent opportunity and foundation for doing this. Based on our understanding, this brief review is to focus on the biochemical pathways of starch synthesis in and implications for breeding programs of cassava, only making a start. 2 Outline of Starch Biosynthesis in Plants Starch biosynthesis in plants usually occurs in the chloroplast of leaves during the day (Martin and Smith, 1995; Orzechowski, 2008; Stitt and Zeeman, 2012). However, this process is involving multi-step catalytic processes by multiple enzymes and further complicated due to the transient synthesis that is also present in other organs such as meristems and root cap cells (Martin and Smith, 1995). No matter how, the key enzymes for starch biosynthesis are, but not limited to, adenosine 5’-diphosphate glucose pyrophosphorylase (AGPase) responsible for the
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