Maize Genomics and Genetics 2025, Vol.16, No.3, 108-118 http://cropscipublisher.com/index.php/mgg 110 In response to these changes, corn plants activate antioxidant defense systems, including enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) to remove excess reactive oxygen species (ROS) (Wu et al., 2020). At the same time, plants also synthesize osmotic regulating substances such as heat shock proteins (HSPs), proline, and soluble sugars to stabilize cell structure and protect protein function. 2.3 Effects on reproductive development and grain yield The reproductive development stage of corn, especially the pollination and filling stages, is extremely sensitive to high temperature stress and is a critical period for determining the final grain yield. Djalović et al. (2023) pointed out that high temperature stress seriously interferes with the pollen formation, pollination process and grain filling mechanism of corn, thereby significantly reducing yield and quality. High temperature can directly damage the anther development process, resulting in decreased pollen vitality, reduced pollen grain number and reduced germination rate. The sensitivity of filaments also decreases with increasing temperature, resulting in delayed silking or drying of filaments, which in turn causes male and female asynchrony and affects the success rate of fertilization. Heat stress can also have a negative impact on pollen tube growth and ovule development, reducing the efficiency of endosperm and embryo formation. During the grain formation stage, high temperature interferes with the transport and distribution of photosynthetic products, causing a decrease in the grain filling rate and a shortened filling duration, resulting in small grains, poor plumpness, and decreased thousand-grain weight. They further emphasized that heat stress not only affects the direct physiological process of yield formation, but also involves imbalances in hormone signals (such as auxin, abscisic acid, and ethylene) and abnormal expression of heat stress response genes. There are obvious differences in the response of different genotypes of corn to high temperature stress during the reproductive stage. Some heat-resistant materials show strong pollen heat tolerance, timely silking ability, and good grain filling stability. The use of genetic variation mining and breeding strategies, such as genomic selection, phenotypic precision screening, and QTL positioning, has become an effective way to improve the heat tolerance of corn in the reproductive stage. 3 Heat-Responsive Genes and Regulatory Networks in Maize 3.1 Heat shock proteins (HSPs) and their role in protein stability Heat shock proteins (HSPs) are a class of highly conserved molecular chaperones that play a key role in maintaining protein stability under high temperature stress conditions. High temperatures often cause protein denaturation or misfolding, leading to cellular dysfunction. HSPs are rapidly induced to express at this time, assisting the correct folding of new proteins, the refolding of damaged proteins, and preventing their aggregation and inactivation. The main HSP families include HSP70, HSP90, HSP60, HSP100 and small molecule heat shock proteins (sHSPs), which play their own unique roles in cell protection. In maize, HSP genes are highly upregulated under high temperature stress, and their expression levels are closely related to the crop's heat tolerance. These proteins not only maintain protein homeostasis, but also interact with membrane systems and organelles to enhance cell structural stability. For example, overexpression of the maize heat shock transcription factor ZmHsf04 in Arabidopsis can significantly upregulate the expression of heat-specific HSP genes, thereby improving the heat tolerance of plants (Jiang et al., 2017). HSPs can also work synergistically with heat shock transcription factors (HSFs) to regulate the expression of other heat stress response genes, forming an important part of the maize heat stress regulatory network. The transcription factor ZmHsf17 further promotes the maintenance of protein stability and membrane integrity under heat stress conditions by regulating phosphatidic acid phosphohydrolases involved in lipid metabolism. 3.2 Transcription factors in heat stress response Transcription factors (TFs) play a key regulatory role in the process of plant response to high temperature stress, and can activate a series of physiological and molecular defense mechanisms by regulating the expression of a large number of stress response genes. Various transcription factor families have important functions in improving plant heat tolerance, mainly including heat shock transcription factors (HSFs), WRKY, NAC, MYB, DREB and bZIP. They provide plants with multi-level heat stress adaptation capabilities by regulating pathways such as
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