Journal of Energy Bioscience 2025, Vol.16, No.5, 248-262 http://bioscipublisher.com/index.php/jeb 254 Sugar signals also work with hormones such as ethylene and jasmonic acid to turn on defense genes and boost ROS response (Morkunas and Ratajczak, 2014). High sugar levels give energy and strengthen cell walls, though some pathogens can still use sugar signals to weaken defenses. 7 Agricultural Applications of Plant Sugar Research 7.1 Improving crop yield by enhancing photosynthesis and sugar flow Gene engineering helps plants use light more efficiently. Scientists improve enzymes like Rubisco and the cytochrome b6f complex to increase CO2 uptake and sugar production. Adding genes from C4 plants such as phosphoenolpyruvate carboxylase or NADP-malic enzyme to C3 crops raises CO₂ near Rubisco, reduces photorespiration, and boosts photosynthesis. Sucrose transporters (SUTs) move sugar from leaves to roots or fruits. When SUT genes are active, plants grow faster and yield more (Li et al., 2020; Croce et al., 2024; Nazari et al., 2024). Improving photosynthesis in the whole canopy also helps crops like rice and wheat produce more biomass, though results depend on species and environment (Wu et al., 2019; Araus, Sanchez-Bragado and Vicente, 2021). 7.2 Genetic engineering to increase starch and sugar storage Key enzymes like starch synthase and branching enzyme control starch buildup. Using CRISPR/Cas9, scientists can edit these genes to make more amylose or resistant starch in rice and maize (Bahaji et al., 2014; Baysal et al., 2020; Zhong et al., 2022). In sugarcane and beets, adjusting enzyme and transporter activity increases sugar storage, but balance with water and nutrients is needed. Modern tools like CRISPR help create crops with higher starch and sugar for food and industry (Patrick et al., 2013; Ahmad and Ming, 2024). 7.3 Sugar metabolism and its effects on fruit and grain quality Sugar metabolism affects sweetness and texture. Levels of sucrose, glucose, and fructose depend on genes and environment. Editing transcription factors like S1-bZIP through CRISPR can make fruits such as strawberries sweeter (Wang et al., 2022a; Du et al., 2024a; 2024b). Conditions like light and temperature also change sugar content. For example, controlling the S6PDH gene in plums raises sugar levels and improves flavor (Chen et al., 2021). 7.4 Applications in bioenergy, biofuels, and industry Sugarcane’s high sugar and biomass make it ideal for bioethanol. CRISPR/Cas9 creates varieties with higher yield and cleaner fuel (Patrick et al., 2013; De Carvalho Silvello et al., 2021; Shi et al., 2023; Ahmad and Ming, 2024). Other crops and microalgae are modified to produce biofuels like ethanol and hydrogen. Turning plant cell walls into sugars for fermentation also supports making bioplastics and other green products. 8 Case Studies on Plant Sugar Metabolism: From Sweeter Taste to Better Stress Resistance 8.1 Case 1: sugar metabolism and sweetness in tomato People like sweeter tomatoes, so increasing sugar content has been a big goal. But when sugar goes up, the fruits often get smaller or yield less. Studies found that two calcium-dependent protein kinases, SlCDPK27 and SlCDPK26, act like “brakes” on sugar levels. They add phosphate groups to sucrose synthase, making it break down faster and slow sugar build-up. When scientists knocked out SlCDPK27 and SlCDPK26, glucose and fructose levels rose by about 30%. The fruits became sweeter, but their size and yield stayed the same. The seeds were smaller and lighter, but germination was normal. This means changing sugar metabolism directly can make fruits sweeter without reducing yield (Wang et al., 2021a; Zhang et al., 2024; Fernie and Martinez-Rivas, 2025). Other teams also improved sugar levels by changing genes for invertase and sugar transporters. Deleting SlINVINH1 and SlVPE5 raised glucose, fructose, and total soluble solids. They also found key QTLs such as Lin5 that affect sugar accumulation. These studies show that plants can use different ways to control sugar metabolism, giving new ideas for improving fruit taste and processing quality (Wang et al., 2021a). Similar work in sugarcane also increased sugar yield, but storage remains a big problem (Patrick et al., 2013).
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