Maize Genomics and Genetics 2025, Vol.16, No.3, 108-118 http://cropscipublisher.com/index.php/mgg 112 catalyzed by ZmRPP13-LK3 may be transported out of the mitochondria through ABC2 and regulate the reverse signaling pathway from mitochondria to the nucleus; cAMP pretreatment significantly improved the survival rate of corn plants under high temperature stress conditions. 4.2 Osmolyte accumulation and membrane stability Heat stress can cause an imbalance in cell osmotic pressure and have a significant impact on the stability of membrane structure. In response to this, corn accumulates osmotic regulating substances (such as proline, betaine, and soluble sugars) to maintain cell turgor, protect the integrity of macromolecular structures, and stabilize the cell membrane system. These osmotic regulating substances can not only act as molecular chaperones to prevent protein denaturation and aggregation under high temperature conditions, but also play an important role in cell osmotic regulation. Heat stress can also induce changes in membrane lipid composition, manifested as an increase in the proportion of saturated fatty acids, thereby reducing membrane fluidity and enhancing membrane stability (Chen et al., 2023). Under high temperature stress conditions, maintaining the integrity of the cell membrane is of vital importance to ensuring the normal physiological function of cells and preventing electrolyte extravasation. 4.3 Heat-induced modifications in photosynthesis and carbon metabolism 4.3.1 Downregulation of photosystem II efficiency and RuBisCO activity Photosystem II (PSII) is very sensitive to high temperatures. Heat stress can damage its oxygen supply complex and reduce electron transfer efficiency, thereby causing a decrease in chlorophyll fluorescence and a decrease in photochemical efficiency (Fv/Fm ratio). At the same time, the activity and stability of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), which is responsible for carbon fixation, are also significantly reduced at high temperatures (Singh et al., 2020; Wu et al., 2020). Heat shock proteins (HSPs) and molecular chaperones play an important role in maintaining the structural stability of these photosynthetic proteins, helping to alleviate heat damage. 4.3.2 Role of C4 metabolism in enhancing heat tolerance C4 plants have shown higher adaptability in evolution. Compared with C3 plants, they have significant advantages in growth rate, carbon dioxide use efficiency and water use efficiency. As a typical C4 plant, corn has a natural physiological advantage in photosynthetic adaptation mechanism. It can fix carbon dioxide more efficiently through the C4 photosynthetic pathway, while significantly reducing water consumption, thereby synthesizing more carbohydrates in a shorter time. Under heat stress conditions, the expression levels of key enzymes in the C4 pathway (such as phosphoenolpyruvate carboxylase PEPC, NADP-malic enzyme and pyruvate phosphate dikinase PPDK) are dynamically adjusted to optimize the carbon assimilation process. This metabolic flexibility enables corn to maintain high photosynthetic efficiency and biomass accumulation capacity in high temperature environments (Djalović et al., 2023; Li et al., 2024). 4.3.3 Regulation of sugar transport and source-sink dynamics Heat stress also affects the distribution and transport of photosynthetic products. Corn maintains an effective source-sink relationship by regulating the expression of sugar transporter genes and phloem loading mechanisms. The enhanced activity of sucrose transporters (SUTs) and SWEETs family members helps transport photosynthetic carbohydrates from leaves to developing grains and roots. Trehalose metabolism also shows an important role in stress signal transduction and energy homeostasis regulation (Liu et al., 2022; Jagtap et al., 2023). 5 Progress in the Inheritance and Breeding of Heat Tolerance in Maize 5.1 Accurately explore heat-resistant germplasm resources and gene loci According to statistics, for every 1 °C rise in global temperature, corn yield will decrease by 7.4%, which is significantly higher than that of rice (reduction of 3.2%). When high temperature stress occurs at the same time as the flowering period of corn, its negative impact will be further aggravated. A large number of studies have focused on the multi-faceted effects of high temperature stress on corn growth and development, including key stages such as flowering pattern, pollen vitality, pollination and fertilization process, and early seed development. The screening of heat-resistant germplasm resources is the primary link in heat-resistant breeding. Technical
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