Maize Genomics and Genetics 2025, Vol.16, No.4, 202-218 http://cropscipublisher.com/index.php/mgg 214 ZmDREB2 in heat-tolerant varieties are believed to enhance the expression of downstream defense genes, thereby reducing the harm of high temperature to pollen and grain development (Figure 2) (Chen et al., 2023). On the contrary, the overactivated ABA/ ethylene signaling module in sensitive varieties leads to accelerated senescence, affecting the yield. Finally, the study functionally verified the identified candidate genes: by knocking out an unknown functional gene that was specifically highly expressed in heat-tolerant varieties with CRISPR/Cas9, the heat tolerance of the transgenic plants significantly decreased, demonstrating that this gene has a positive effect on the heat resistance of corn. This case demonstrates that transcriptome comparison can effectively reveal the differences in molecular responses between heat-resistant and sensitive varieties, from which potential key heat-resistant factors can be identified. When applying these genes to breeding, molecular marker-assisted selection of materials carrying favorable alleles can be adopted, or the genotypes of sensitive varieties can be directly improved through transgenic/gene editing. For instance, the favorable allele of ZmHsfA2 discovered above can be tracked and selected in the breeding population through molecular markers, thereby enhancing the heat tolerance of the new combination. Introducing the heat-resistant version of the ZmDREB2 gene into sensitive varieties may also enhance their heat resistance. It can be seen that the variety comparison study combining transcriptomics and functional genomics methods has provided clear molecular targets and improvement ideas for the cultivation of heat-tolerant corn, accelerating the process of genetic improvement. Figure 2 The effects of heat stress on maize kernel weight (Adopted from Chen et al., 2023) Image caption: (A) Radar chart of the average kernel weight of the 494 maize inbred lines. (B) Histogram of average kernel weight of PF5411-1 and LH150. (C) Ear and kernel phenotype of PF5411-1 and LH150 under normal and heat stress conditions. (D) Histogram of hundred kernel weight of PF5411-1 and LH150 under normal and heat stress conditions. “CK” represents control group, “HT” represents heat stress group, the same below. Scale bar for ears in C is 5 cm, and scale bar for kernels in C is 1 cm. ** indicate a significant difference between the two sets (p < 0.01), ANOVA was used to analyze significance (Adopted from Chen et al., 2023)
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