Maize Genomics and Genetics 2025, Vol.16, No.3, 129-138 http://cropscipublisher.com/index.php/mgg 134 example, a study by Chen et al. (2023) identified 770 commonly up-regulated and down-regulated genes in maize kernels under high temperature stress, and predicted 41 putative TFs, indicating that pathways such as protein processing in the endoplasmic reticulum and ethylene signaling play a key role in heat tolerance. Many genes in maize kernels that respond to heat stress were identified, and 7 genes and 4 pathways that were highly correlated with maize kernel heat tolerance were found. Genome-wide association analysis (GWAS) provides an important means to identify potential heat-resistant QTLs and dominant genes, and to select superior maize varieties for enhanced stress resistance (Djalović et al., 2023). Inghelandt et al. (2019) identified six QTLs, each of which individually explained 7% to 9% of the phenotypic variance, all of which explained a significant portion of the phenotypic variation associated with heat tolerance, highlighting the genetic diversity that can be used in breeding programs. 5.2 Molecular regulation of heat tolerance pathways The molecular regulatory mechanism of heat tolerance involves a complex signaling network, including the participation of heat shock proteins (HSPs) and transcription factors (TFs). The expression of heat shock factors (HSFs) and HSPs is a widely studied heat tolerance response in transgenic maize, which can significantly enhance the tolerance of plants to high temperature stress. HSPs are not only key regulators of plant heat stress response, but also play an important role in plant reproductive development and response to various adversities. For example, the ZmNAC074 transcription factor provides a key candidate regulatory gene for the regulation and genetic improvement of maize heat stress tolerance by regulating the accumulation of stress metabolites and upregulating the expression of reactive oxygen species (ROS) scavenging genes (Xi et al., 2022). Among the heat-tolerant maize lines, a total of 35 common regulatory genes overlapped in five maize inbred lines, and the expression of genes related to protein folding and temperature stimulus response was significantly upregulated, indicating that the genetic response of maize to high temperature stress is highly coordinated (Xue et al., 2024). 5.3 Transcriptional and post-transcriptional regulation Transcriptional and post-transcriptional regulatory mechanisms play a key role in the heat stress response of maize. Researchers can conduct molecular regulatory network mechanism research on the response of maize to heat stress and explore key regulatory genes with great utilization value. Members of the transcription factor family such as AP2, MYB and WRKY are involved in regulating the expression of heat-responsive genes. The up-regulated genes identified in the heat-tolerant inbred CML 25 will become potential candidate genes for the development of heat-tolerant maize using marker-assisted backcross breeding (Jagtap et al., 2023). Transcriptional kinetic analysis of maize leaves, pollen and ovules under heat stress conditions showed that their gene expression profiles changed significantly, and some genes showed more significant expression characteristics in heat-tolerant inbred lines. Metabolic overview pathways and secondary metabolite biosynthesis pathways involved 264 and 146 genes, respectively, which were highly enriched in heat stress response. The study by Liang et al. (2022) also identified cis- and trans-expression quantitative trait loci (eQTLs), which regulate genotype-specific heat stress responses by affecting promoter activity and transcription factor binding ability, providing an opportunity to better characterize the transcriptome responses of important genotypes that may produce important genotypes through environmental interactions. 6 Case Study: Regional Impact and Genetic Response of Heat Stress in Maize 6.1 Field observations in heat-prone areas In heat-prone areas such as the North China Plain and sub-Saharan Africa, maize is frequently subjected to heat stress, which has a significant impact on its reproductive development and yield formation. Field trials on maize cultivation have shown that the suitable daily average temperature for maize grain filling is 22 ℃-24 ℃, and high temperature stress during the reproductive and grain filling periods can lead to a significant decrease in yield. Under high temperature stress conditions, phenotypic traits such as leaf wilting, male tassel sterility, and anthesis-silking interval (ASI) are negatively correlated with grain yield, while pollen shedding time and fruiting rate are positively correlated with yield (Alam et al., 2017). These research results highlight the urgent need to develop heat-resistant maize varieties in heat-prone areas to maintain stable production in response to the increasing risk of heat stress in maize.
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