Maize Genomics and Genetics 2025, Vol.16, No.3, 119-128 http://cropscipublisher.com/index.php/mgg 125 The study achieved remarkable results, identifying five haplotype regions and eight important SNP variant sites that are closely associated with maize yield under heat stress. In addition, the CIMMYT Asia research team validated the above GWAS results in an independent biparental breeding population and confirmed 22 genomic regions associated with maize yield and related secondary agronomic traits under heat stress (Kamweru et al., 2022). These validation results not only enhance the reliability of GWAS results, but also provide actionable molecular marker resources for heat-resistant breeding. Through integrated analysis of multiple genetic background populations, the study further identified three major QTL intervals with significant effects in a variety of high-temperature-related traits. These QTL regions can be used as priority genetic resources in future breeding programs and have good breeding application prospects. It is worth mentioning that CIMMYT's research has also expanded to lipid-related traits and field phenotypic performance under high temperature and non-stress conditions. The study found 78 significant SNP associations at 40 loci, involving 53 candidate genes, which further enriched the genetic map of heat-resistant traits and strengthened the association basis between phenotype and genotype. The joint study clearly revealed the multi-gene control characteristics of maize yield traits under high temperature or combined stress (such as drought+high temperature) conditions. The research team pointed out that in this complex genetic control background, the use of whole genome prediction (genomic prediction, GP) will be the best way to improve yield performance and breeding efficiency (Kamweru et al., 2022). By integrating GWAS data with GP models, we can not only improve the accuracy of selection, but also accelerate the breeding of heat-resistant varieties, providing scientific and technological support for coping with future climate uncertainties. 5.2 ZmHSF20 regulatory network analyzes the molecular mechanism of heat tolerance in maize Against the background of climate warming and increasing frequency of high temperature stress, analyzing the molecular regulatory mechanism of crop heat tolerance has become an important topic in maize genetic improvement research. The team of Zhang Mei, a researcher at the Institute of Botany, Chinese Academy of Sciences, conducted research on the "functional mechanism of core transcription factors of maize heat tolerance", constructed a systematic high temperature stress transcriptome map, and successfully identified the key regulatory factor-heat shock transcription factor ZmHSF20 through co-expression network analysis (Li et al., 2024). The results of co-expression analysis showed that the ZmHSF family and the ethylene response factor (ERF) family were highly enriched in the "heat response" module, among which ZmHSF20 was confirmed as the core regulatory factor. In order to verify its function, the researchers constructed Zmhsf20 deletion mutants and ZmHSF20 overexpression lines. Phenotypic analysis results showed that ZmHSF20 overexpressing plants were more sensitive to high temperature stress, while the heat tolerance of Zmhsf20 mutants was significantly enhanced, clarifying the function of ZmHSF20 as a negative regulatory factor in corn to inhibit heat tolerance (Figure 1) (Li et al., 2024). In-depth mechanism studies found that ZmHSF20 affects the heat tolerance of plants by downregulating the expression of target genes ZmCesA2 (cellulose synthase) and ZmHSF4 (another heat shock transcription factor). Experiments have confirmed that ZmHSF4 has the function of transcriptionally activating ZmCesA2, and overexpression of ZmCesA2 and ZmHSF4 can improve the heat tolerance of corn (Li et al., 2024). Zmhsf4 mutants are more sensitive to heat stress, further verifying the positive role of ZmHSF4 in heat tolerance regulation. The constructed Zmhsf20-1Zmhsf4-1 double mutant further proved the downstream position of ZmHSF4 in the ZmHSF20 regulatory pathway. In addition, ultrastructural observations showed that the Zmhsf20 mutant and the ZmHSF4 overexpression strain had a more stable cell wall structure under high temperature. The study also found that ZmHSF20 regulates ZmCesA2, thereby affecting the expression of cell wall-related genes such as ZmPAL1, participating in the cell wall construction process, and further improving the stability of cell structure under heat stress.
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