Maize Genomics and Genetics 2025, Vol.16, No.4, 202-218 http://cropscipublisher.com/index.php/mgg 211 upregulated 1-2 hours after high temperature and remained so for a relatively long time. In addition, pretreatment with high-temperature stress can induce a "thermal memory" effect, enabling some defense genes to remain highly expressed even after the stress is lifted, so as to respond more quickly when the temperature returns later. For example, although the expression levels of ZmHSP17 and ZmHSP101 genes decreased after the first high temperature, they were still higher than those of the untreated control, and could be upregulated more rapidly at the second high temperature (Li et al., 2022). Other studies have shown that different heat-resistant varieties have differences in the dynamics of gene expression: heat-resistant materials tend to activate defense genes earlier and maintain their high levels of expression for a long time, while the response of sensitive materials may be lagging and not long-lasting. In conclusion, the expression of maize heat response genes has distinct temporal dynamic characteristics. From instantaneous response to continuous response and then to adaptation and recovery, the gene networks at each stage are interconnected. This suggests that when studying the heat tolerance mechanism of corn, we should combine the time dimension and capture the molecular events at key time points. In breeding selection, indicators such as the residual level of gene expression after thermal shock treatment can also be used to evaluate the thermal memory ability and thermal durability of materials. 5.3 Coordinated mechanisms of spatial and temporal gene regulation The resistance of corn to high-temperature stress is the result of the coordinated action of its various tissues at different time scales, that is, spatial regulation and temporal regulation are closely combined. The division of labor and complementarity of different parts of the plant in high temperatures enable corn to enhance its overall heat resistance. For instance, when high temperatures strike, leaves rapidly synthesize HSP and other substances to protect their own cellular functions, while the root system can send drought/heat combined signals to the above-ground parts through hormones such as ABA, causing stomata to close and reducing water loss. This synergy between roots and leaves helps the plant survive short-term extreme high temperatures. On a longer time scale, the heat responses at different periods also need to be coordinated: the protective and restorative mechanisms strengthened during the seedling stage may lay the foundation for heat resistance in the later reproductive stage. For instance, the heat shock proteins and other substances produced by high-temperature pretreatment during the seedling stage remain at a certain level within the plant. When the plant enters the tasseling and flowering stage, these chaperone proteins may still exist, thereby enhancing the pollen's tolerance to high temperatures. This reflects the influence of temporal "memory" on spatial resistance. In addition, the specificity of gene expression in space is itself regulated by temporal factors. Take the male ears of corn as an example. The spike differentiation period and the flowering period are the two time Windows that are most sensitive to heat. The damage caused by high temperature to the male ears during these two stages is greater than that during the vegetative growth period. Studies show that high temperatures during the spikicle differentiation period can reduce the number of small flowers in male spikes, while high temperatures during the flowering period can lower pollen vitality and the amount of pollen released. Therefore, only by protecting the right tissue at the right time can the best heat resistance effect be achieved. This requires precise spatio-temporal expression regulation (Liu et al., 2023). For instance, the continuous expression of the ZmHSFA2 gene in corn leaves is crucial for heat tolerance, but in organs such as filaments and grains, it may only need to be expressed at specific stages. For instance, some mirnas and hormone signals may move over long distances between roots, stems and leaves, playing a coordinating role across tissues. Cross-tissue signals and local gene regulation jointly form the regulatory network of heat resistance throughout maize plants. In future research, integrating multi-omics data from different tissues and at different time points is expected to construct a spatio-temporal regulation model for corn's response to high-temperature stress, revealing the contribution of each tissue to heat resistance at each growth stage. This also has guiding significance for formulating agricultural defense strategies: for instance, cultivation measures can be taken to avoid high temperatures during the most sensitive flowering and grain stage of corn, and during the seedling stage, plants can be trained to acquire heat tolerance memory. Furthermore, the synergy of spatio-temporal expression also reminds us that in the evaluation of heat-tolerant breeding, we should comprehensively examine the heat resistance performance of materials at different growth stages and in different organs to screen out truly comprehensively heat-tolerant strains. The heat tolerance mechanism of corn is a complex spatio-temporal coordinated regulation process, which requires not only the mutual cooperation of
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