Plant Gene and Traits 2024, Vol.15, No.3, 108-117 http://genbreedpublisher.com/index.php/pgt 109 the potential to enhance starch production in cassava, providing a promising avenue for biofortification and yield improvement (Ihemere et al., 2006). By integrating recent findings from genomic studies, pathway reconstructions, and transgenic approaches, this review aims to provide a comprehensive understanding of starch biosynthesis in cassava. Such knowledge is instrumental for the development of improved cassava varieties with enhanced starch quality, which can have significant impacts on food security and industrial applications. 2 Biochemical Pathways of Starch Synthesis in Cassava 2.1 Overview of starch synthesis: general steps in starch biosynthesis in plants Starch biosynthesis in plants is a complex process involving the conversion of glucose units into starch polymers. This process begins with the synthesis of adenosine diphosphate glucose (ADP-glucose), which serves as the activated glucose donor for the synthesis of amylose and amylopectin, the two main components of starch. The biosynthesis pathway includes the action of several key enzymes such as ADP-glucose pyrophosphorylase (AGPase), starch synthase (SS), starch branching enzyme (SBE), and de-branching enzyme (DBE) (Li, 2024), which work in concert to form the highly organized structure of starch granules (Figure 1) (Tappiban et al., 2019). Figure 1 Schematic mechanism of starch biosynthesis in cassava storage root (Adopted from Tappiban et al., 2019) Image caption: Abbreviations of enzymes are as follows: sucrose synthase (SuSy), UDPG pyrophosphorylase (UGPase), cytosolic phosphoglucomutase (cPGM), plastidial phosphoglucomutase (pPGM), fructokinase (FRK), cytosol phosphoglucose isomerase (cPGI), adenosine diphosphate glucose pyrophosphorylase (AGPase), granule bound starch synthase (GBSS), starch synthase (SS), starch branching enzyme (SBE), de-branching enzyme (DBE) and glucan, water dikinase (GWD). The membrane transportors are sucrose transporters (SUT), glucose 6-phosphate/phosphate transporter (GPT or G6PPT), ATP/ADP transporter (AATP) and ADPG translocator. Enzyme substrates and products including glucose 6-phosphate (G6P), adenosine Triphosphate (ATP), adenosine monophosphate (AMP), fructose 6-phosphate (F6P), uridine diphosphate (UDP), uridine diphosphate glucose (UDPG), pyrophosphate (PPi), orthophosphate (Pi), glucose1-phosphate (G1P), uridine triphosphate (UTP) and malto-oligosaccharide (MOS) (Adopted from Tappiban et al., 2019) Figure 1 provides a detailed schematic representation of the starch biosynthesis pathway in the cassava storage root. This diagram includes various enzymatic steps and metabolic processes that occur within the plant's cells to convert basic sugar molecules into complex starches, which are stored in the roots.
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