Journal of Energy Bioscience 2025, Vol.16, No.5, 248-262 http://bioscipublisher.com/index.php/jeb 251 Adp-glucose pyrophosphorylase (AGPase) is a key enzyme in starch synthesis, activated by 3-phosphoglyceric acid, inhibited by inorganic phosphoric acid, and regulated by REDOX (Qu et al., 2018). Sucrose synthase (SuSy) can break down sucrose into UDP- or ADP- glucose and fructose. Different types of SuSy are involved in cellulose synthesis, stress resistance and growth in different parts of plants (Stein and Granot, 2019; Li et al., 2024). 3.4 Genetic regulation of carbohydrate biosynthesis The expression of enzymes such as SPS, AGPase and SuSy is controlled by multiple transcription factors, such as bZIP, MYB, AP2/ERF, which respond to changes in glucose concentration, hormones and environment (Ma et al., 2017; Yoon et al., 2021; Finegan et al., 2022; Li et al., 2024a). In cassava, MebHLH68 links ABA signaling to glucose metabolism genes and regulates sucrose and starch pathways (Li et al., 2024c), while AREB2 activates glucose storage-related genes under stress (Ma et al., 2017). Sugars can also act as signal molecules. Sucrose and trehalose 6-phosphate affect gene expression by regulating SnRK1 kinase (Baena-Gonzalez and Lunn, 2020; Wang et al., 2020; Gobel and Fichtner, 2023). The perception of glucose depends on hexokinase, which regulates metabolism according to energy levels (Stein and Granot, 2019; Finegan et al., 2022). Studies have shown that when the corn starch synthesis gene changes, the sugar transport gene also responds rapidly (Finegan et al., 2022). 4 Sugar Metabolism and decomposition pathways in Plants: Integration of energy, Transport and Regulation 4.1 Glycolysis and respiratory metabolism Glycolysis breaks down glucose and other sugars into pyruvate and generates ATP and NADH, which is completed in the cytoplasm. This provides rapid energy for plants and also offers raw materials for the synthesis of amino acids and fats. Subsequently, pyruvate enters the mitochondria to undergo the TCA cycle and continues to generate ATP. Glycolysis, in conjunction with respiration, converts stored sugar into energy, which is particularly important when plants have high energy demands or are under stress (Rolland et al., 2006; Smeekens and Hellmann, 2014). Sugar concentration, light, temperature and other factors can all affect enzyme activity. Sugar is not only an energy source, but also can act as a signaling molecule to regulate gene expression and help plants maintain balance during growth and stress (Koch, 2004; Rolland et al., 2006; Smeekens and Hellmann, 2014). 4.2 Glucose Transporters and cellular compartmentalization Plants transport sugar from leaves to roots, seeds and other parts through sugar transporters. The main types include sucrose transporter (SUT), SWEET protein and monosaccharide transporter (MST). SUT is responsible for long-distance transportation, SWEET regulates the inflow and outflow of sugar, and MST trantransport glucose and fructose (Selvam et al., 2019; Saddhe et al., 2020; Xue et al., 2021; Garg and Kuhn, 2022). These proteins are distributed in the cell membrane, vacuole membrane and endoplasmic reticulum, and can regulate the flow of sugar inside and outside the cell. They are influenced by protein interactions, signal molecules and the environment, thereby flexibly controlling sugar transport under different conditions (Saddhe et al., 2020; Xue et al., 2021; Garg and Kuhn, 2022). 4.3 Sugar metabolism and amino acid and lipid synthesis The intermediate products of glycolysis can be used for amino acid synthesis, and acetyl-coenzyme A participates in the synthesis of fatty acids and lipids. When sugar is insufficient, gluconeogenesis converts amino acids or lipid metabolites back into sugar for energy supply, especially during seed germination or when energy is insufficient (Walker, Chen and Famiani, 2021). Glucose signals such as T6P can regulate enzymes and transcription factors of lipid metabolism and also affect the activity of amino acid synthesis genes (Zhai et al., 2021).
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