Maize Genomics and Genetics 2025, Vol.16, No.4, 202-218 http://cropscipublisher.com/index.php/mgg 205 heat stress response of maize. High-temperature stress regulates the metabolism and signal transduction of various plant hormones such as ABA, triggering a series of downstream responses, thereby guiding resource reallocation, inhibiting growth and activating stress protection mechanisms in corn seedlings. 3 Expression Characteristics of Heat-Responsive Genes 3.1 Expression patterns and protective roles of heat shock protein (HSP) families Heat Shock Protein (HSP) is a type of molecular chaperone protein that is abundantly expressed in plants under adverse conditions such as high temperature. It is widely present in crops such as corn and plays an important protective role in heat tolerance. According to molecular weight, the HSP family is classified into subcategories such as HSP100, HSP90, HSP70, HSP60, and small molecule HSP (sHSP). Among them, small-molecular-weight HSPS (such as HSP17.9, HSP18, etc.) accumulate most significantly under high-temperature induction. Transcriptome analysis indicates that high-temperature stress can cause a strong upregulation of a large number of HSP genes in corn: for instance, after the B73 seedlings of the corn inbred line were treated at 45 ℃ for one hour, the transcriptional levels of as many as dozens of HSP genes increased several times or more. Especially the HSP70 family and the small HSP genes of HSP17-30kDa are extremely sensitive to temperature changes. Their promoters often contain thermal shock elements (HSE), which can be rapidly activated by the binding of thermal shock transcription factors. The high expression of these HSPS at high temperatures serves to act as molecular chaperones, facilitating the refolding, assembly and transport of damaged proteins within cells, preventing the aggregation of non-natural conformational proteins and thereby reducing cytotoxicity. For instance, small HSPS such as ZmHSP16.9 and ZmHSP18 in corn accumulate in large quantities under heat stress, which can effectively bind to denatured proteins and maintain some of their structures. Once the stress is relieved, they assist in their reconstitution. HSP70 and HSP90 are mainly located in the cytoplasm and organelles, helping to stabilize various functional protein complexes. A study on the HSP90 gene family in corn identified nine ZmHSP90 genes and found that they exhibited tissue-specific induced expression patterns under different heat stress conditions and were involved in protein folding and the assembly of signal complexes. As a member of the HSP100 family, HSP101 also plays a significant role in the heat-sensitive process of meiosis in pollen mother cells. Li et al. (2022) reported that ZmHSP101 is highly expressed during the formation of corn microspores and helps maintain the protein homeostasis of pollen mother cells. The loss of its function can lead to male sterility at high temperatures. These pieces of evidence indicate that different types of HSPS play their respective roles in the heat tolerance of corn: small HSPS are responsible for the immediate "emergency rescue" of damaged proteins, HSP70/HSP90 and others maintain normal cell metabolism and the operation of signaling pathways, and HSP100 is involved in heat memory and long-term adaptation. Therefore, the high expression pattern of HSP family genes is a typical "fingerprint" feature of corn in response to high-temperature stress, and its products endow plant cells with heat protection at the cellular level through molecular chaperone mechanisms 3.2 Regulatory functions of heat-responsive transcription factor families (HSF, bZIP, NAC, etc.) Transcription factors are crucial regulatory elements in the process of heat stress signal transmission. A series of studies have identified multiple families of transcription factors involved in the thermal response of corn, including thermal shock transcription factor (HSF), basic leucine zipper protein (bZIP), NAC, AP2/ERF, WRKY, etc. Among them, the HSF family is a central regulator that directly senses protein denaturation signals and triggers the expression of downstream defense genes. The maize genome contains over 25 HSF genes, and their expression profiles under high-temperature stress are complex: most HSFS are rapidly upregulated and activated, such as ZmHSF01 and ZmHSF06, whose mRNA increases sharply within a few minutes of thermal stimulation, while a few negatively regulated HSFS are also induced. ZmHSF20 is a core heat shock transcription factor discovered in recent years, and it belongs to the B2 class of HSF. Li et al. (2024) identified ZmHSF20 through heat stress transcriptome co-expression network analysis. Functional studies demonstrated that it plays a negative regulatory role in maize heat tolerance: overexpression of ZmHSF20 instead reduces the survival rate of seedlings, while knockout of ZmHSF20 significantly improves maize heat tolerance. Mechanism, ZmHSF20 directly binds to inhibit the promoter activity of another heat-resistant HSF - ZmHSF04, as well as the expression of cellulose synthetase ZmCesA2, thereby balancing the resource allocation between growth and defense (Figure 1). In
RkJQdWJsaXNoZXIy MjQ4ODYzNA==