PLANT SCIENCE TODAY Vol 12(sp1): 01–10 https://doi.org/10.14719/pst.10208 eISSN 2348-1900 REVIEW ARTICLE
Heat stress tolerance in maize - An overview Hemaswi Shinde1, Kumari Vinodhana N2*, Sivakumar S2, Vanitha K3 & Kathirvelan P4 1
Department of Genetics and Plant Breeding, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India 2 Department of Millets, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India 3 Department of Fruit Science, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India 4 Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India *Correspondence email - kumarivinodhana@tnau.ac.in
Received: 24 June 2025; Accepted: 08 August 2025; Available online: Version 1.0: 26 September 2025 Cite this article: Hemaswi S, Kumari VN, Sivakumar S, Vanitha K, Kathirvelan P. Heat stress tolerance in Maize - An Overview. Plant Science Today. 2025;12(sp1):01–10. https:/doi.org/10.14719/pst.10208
Abstract Maize (Zea mays L.), one of the world’s most important staple crops, is increasingly vulnerable to rising temperatures and erratic climatic conditions. Among various abiotic stressors, heat stress stands out as a critical factor that disrupts the crop’s growth by impairing morphological, physiological, biochemical and molecular processes ultimately leading to substantial yield losses. The severity of this issue is expected to escalate with the intensification of global warming and water scarcity. To ensure sustainable maize production, there is an urgent need to develop heat-resilient, high-yielding hybrids. This review explores recent advances in identifying thermotolerant donor lines and employing them in hybrid development. Emphasis is placed on integrated strategies, including advanced agronomic interventions, molecular breeding, CRISPR/Cas-based genome editing and the application of multi-omics platforms transcriptomics, proteomics, metabolomics and phenomics to decipher heat-responsive mechanisms. Furthermore, the integration of high-throughput phenotyping, machine learning and climate-smart agricultural practices offers promising pathways to accelerate breeding efficiency and improve field-level adaptation. By synthesizing these cutting-edge approaches, this review provides a comprehensive framework to mitigate the adverse impacts of heat stress and support climate-resilient maize cultivation in the face of future challenges. Keywords: advanced genomic tools; heatomics; heat shock protein; maize; thermo-resilience
Introduction Climate change poses a serious threat to humanity, with rising temperatures, floods and disease outbreaks impacting global food security. Among these, global warming significantly affects agriculture, endangering livelihoods as millions depend on farming for survival. In general, plants are exposed to a variety of environmental conditions, consisting of heat, drought and saline stress. Amongst which, heat stress exerts a profound negative impact. The progressive increase in global climate change, caused by extreme heat waves and intermittent drought is a major concern for crop production (1). Heat stress refers to a rise in temperature beyond the optimal range, causing irreversible damage to crop growth and development. The heat stress severely affects the crop during seedling and reproductive stage (2). Globally, heat stress compromises the productivity and resilience of major crops viz., rice, wheat, maize and soyabean. In case of Wheat (Triticum aestivum L.), global production is decreased by more than 6 % (3). In the USA, there is a significant reduction in yield loss of Maize (> 9 %), followed by China (> 7 %) and India (> 4 %) (4). Heat stress has emerged as a major limiting factor in agriculture, adversely affecting crop growth and productivity by disrupting morphological, physiological, biochemical and molecular processes (5). It leads to reduced seed germination,
stunted growth, leaf damage, impaired reproductive development and ultimately a decline in yield. To cope with these challenges, there is an urgent need to develop climate-resilient crop varieties. This includes adopting stress avoidance strategies such as altering plant architecture, leaf orientation and growth duration, along with deploying advanced genetic tools like mutagenesis, markerassisted selection, genome editing and quantitative trait loci (QTL) mapping to improve stress tolerance (6). In addition to genetic improvements, agronomic practices like optimal soil and nutrient management, crop rotation, precise sowing time and irrigation scheduling can help mitigate heat-related damage. Furthermore, the external application of protective agents such as osmoprotectants, antioxidants, phytohormones, polyamines and heat shock proteins (HSPs) has shown potential in alleviating heat stress effects in crops (7). Impact of climate change on maize Maize (Zea mays L.) is a tall, determinate, annual C4 crop widely cultivated across the globe for its diverse uses in food, animal feed and industrial applications. Owing to its adaptability and productivity, maize contributes approximately 40 % of the total global cereal production (FAO, 2023) (8). However, the increasingly erratic climatic patterns, including rising temperatures and prolonged dry spells, have made it difficult to sustain crop productivity. According to projections by the Intergovernmental
Panel on Climate Change (IPCC), the global mean temperature is expected to rise by 0.3 °C between 2025 and 2100 (9), posing serious challenges to crop growth. In maize, the detrimental effects of heat stress are evident across all developmental stages from germination to maturity manifesting as reduced leaf area, lower net photosynthetic efficiency, decreased biomass accumulation, pollen sterility, poor grain set and ultimately reduced grain yield and quality (4). These impacts are particularly severe during sensitive phases like tasselling and grain filling. Given the growing urgency of climate adaptation in maize, this review aims to provide a comprehensive synthesis of heatinduced changes at morphological, physiological, biochemical and molecular levels. It focuses on identifying key traits linked to thermotolerance and compiles current strategies including stressresponsive breeding, omics technologies, gene expression regulation, genome editing and adaptive agronomic practices. The objective is to present an integrative framework that can support the development of heat-resilient maize cultivars suitable for changing climatic conditions. A systematic literature review was conducted using scientific databases like Scopus, Google Scholar and Web of Science with relevant keywords to ensure up-to-date and evidence-based insights. Heat stress response framework in plants is depicted in Fig. 1 Response of plant to heat stress Morphological adaptations
The plant's life cycle is broadly categorized into two phases: the vegetative stage, comprising seed emergence, root, stem and leaf development; and the reproductive stage, including flowering and grain filling (Fig. 2). Both stages are highly sensitive to heat stress, although the reproductive phase is often more critically affected due to its direct influence on fertilization and yield (8). High temperatures, especially in tropical zones, result in notable yield losses by impairing reproductive structures and processes. For instance, maize genotypes with high leaf wax content, lower cob and leaf angle and compact tassels have shown better adaptation under elevated temperatures, as these traits reduce direct solar radiation exposure and evaporation.
Heat stress leads to structural injuries such as leaf sunburn, shoot inhibition, abscission and fruit discoloration, ultimately lowering marketable yield (Fig. 1). It can extend the grain-filling period, resulting in smaller kernels and decreased grain weight and density (9). The nutritional quality of maize kernels including carbohydrate, protein and oil content also declines under heat stress. Additionally, anatomical changes such as smaller cell size, reduced internode length, stomatal closure, increased stomatal and trichome density and wider xylem vessels in both roots and shoots help conserve water and sustain growth under high temperatures. At the sub-cellular level, elevated temperatures disrupt organelle functions, leading to impaired cell division and expansion (10). Heat stress during flowering may cause irreversible damage, including floral abortion and reduced pollen viability, thus hindering fertilization and seed development (11). Physiological changes
The morphological responses to heat stress are closely tied to a cascade of physiological adjustments that help plants survive under elevated temperatures. Key physiological parameters such as membrane fluidity, photosynthetic rate, respiration, osmolyte accumulation and hormone balance are significantly disrupted (12). Heat stress also alters stomatal conductance, disturbing the normal gas exchange processes and leading to reduced tissue water potential, which ultimately affects plant water status and photosynthetic efficiency (13). Critical traits including seed germination, root elongation, leaf expansion and the anthesis-silking interval (ASI) are compromised, particularly during flowering and grain filling, thereby reducing both grain quality and yield potential (14). Maintaining a high photosynthetic rate under stress is considered a major physiological mechanism for heat tolerance, as it directly influences biomass and economic yield (15). Selection of heat-responsive traits such as leaf area, elongation rate, photosynthetic capacity and reproductive characteristics like kernel number per row, tassel sterility, pollen viability and stigma receptivity have proven useful in maize breeding
Fig. 1. Main impacts of high temperature on plants. https://plantsciencetoday.online 3 programs (16). Trait-based phenotyping, especially under environment-specific stress conditions, is one of the most effective strategies to screen and select tolerant genotypes (17, 18). The integration of advanced tools such as robotics and artificial intelligence has further enhanced the precision and efficiency of phenotyping under field conditions (19). Other relevant physiological indicator heats include chlorophyll fluorescence parameters (e.g., Fv/Fm ratio) reflecting photoinhibition and canopy temperature depression (CTD), which correlates with transpiration efficiency and yield stability. Heat stress also impairs mitochondrial respiration and ATP synthesis, causing cellular energy imbalance. Plants accumulate compatible solutes such as proline, glycine betaine and soluble sugars to stabilize membranes and maintain osmotic balance. Hormonal signalling, especially involving abscisic acid (ABA), salicylic acid and ethylene, is crucial for stress perception and response.
A robust antioxidant system is essential for heat tolerance. Enzymes like superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) play critical roles in scavenging reactive oxygen species (ROS). SOD converts superoxide radicals (O₂-) into hydrogen peroxide (H₂O₂), which is further detoxified by CAT and APX, thereby protecting cellular structures from oxidative damage. Elevated activity of these enzymes is commonly associated with enhanced thermotolerance in maize genotypes. Additional mechanisms such as increased cuticular wax deposition reduce transpirational water loss and prevent overheating. The stay-green trait, which prolongs photosynthetic activity under heat stress, also contributes to yield stability. Nevertheless, thermotolerance remains a complex and multigenic trait influenced by physiological plasticity and genotype × environment interactions (13). Schematic representation of heat stress effects on maize during vegetative and reproductive growth stages is given below in Fig. 2.
Heat stress triggers a cascade of physiological disruptions at the cellular level, primarily through the generation of highly reactive and toxic oxygen species (ROS) (20). These oxygen radicals disturb the delicate cellular equilibrium by attacking vital macromolecules and compromising both cellular and subcellular membrane integrity (21). In response, plants have evolved sophisticated defence systems against oxidative stress, including an arsenal of enzymes, proteins, vitamins and secondary metabolites collectively known as antioxidants (20). Numerous studies have confirmed that higher levels of antioxidants are linked with improved thermal tolerance. By modulating the activity of key antioxidative enzymes, plants can effectively mitigate oxidative damage under heat stress (22). These antioxidative enzymes (e.g., superoxide dismutase, catalase and peroxidases) safeguard plants by neutralizing toxic ROS, while non-enzymatic antioxidants (e.g., ascorbate, glutathione, tocopherols) play critical roles in redox homeostasis and signal transduction (23). Ascorbate, for instance, not only functions as a cofactor for various enzymes but also regulates physiological processes and the synthesis of other protective molecules like tocopherols (24). While H₂O₂ is typically harmful at high concentrations, it also acts as a signalling molecule that activates stress-responsive pathways in plants (25). In addition to antioxidant defences, plants accumulate a suite of low-molecular-weight compounds, collectively called osmolytes, which significantly contribute to stress tolerance under extreme temperatures (26). These osmolytes including sugars, proline, ammonium compounds, sulphonium derivatives, glycinebetaine and trehalose stabilize proteins and membranes, preserve enzyme function and maintain cell turgor during stress. One of the most studied osmolytes, glycine-betaine (GB), accumulates in response to abiotic stress and plays a vital role in membrane protection and enzyme stabilization (26). Interestingly, its biosynthesis varies across species; for example, maize produces
Fig. 2. Schematic representation of heat stress effects on maize during vegetative and reproductive growth stages. Plant Science Today, ISSN 2348-1900 (online) HEMASWI ET AL 4
higher GB levels compared to sugarcane (27). Moreover, osmolytes not only protect cells but also serve as metabolic signals, triggering gene expression linked to stress adaptation. Their accumulation is tightly regulated by complex metabolic pathways, many of which have been identified as quantitative trait loci (QTLs) useful in stress-tolerant breeding. Through marker-assisted selection (MAS) and genetic engineering, breeders can enhance osmolyte biosynthesis in elite cultivars (3). Several studies have demonstrated that overexpression of key biosynthetic genes leads to higher osmolyte content and improved thermotolerance in transgenic plants. Additionally, osmolytes aid in maintaining photosynthetic efficiency under heat stress by protecting chloroplast structure and reducing photoinhibition. They also contribute to stomatal regulation, ensuring better water-use efficiency. Some osmolytes, such as proline and trehalose, have been shown to act as chemical chaperones, stabilizing unfolded proteins during thermal stress. Recent research even suggests that osmolyte accumulation enhances plant immune responses, indirectly contributing to overall stress resilience. Molecular mechanisms
In molecular approach, the heat shock protein, advanced genomics and omics technology plays a major role. Plant cell organelles have an effective heat sensing mechanism that generates a signalling cascade for quick adaptive changes (28). The plasma membrane contains Ca2+ conducting channels known as cyclic nucleotide-gated ion channels (CNGCs) (29). In maize, 11 plasma membrane localized CNGC genes play a significant role in heat tolerance (30). Heat stress causes an increase in the production of specific proteins known as Heat Shock Proteins (HSPs), which maintain protein stability and help retain their original structure under stressful conditions. These proteins act as molecular chaperones and are vital for protecting plant cells from heat-induced damage by preventing misfolding and aggregation of proteins (3). Role of different HSPs in maize is described in Fig. 3 Firstly, Vierling in 1991 proposed the significance of HSPs
in plants. Based on the molecular weight, they are categorized into five conserved classes, viz., Small Heat Shock Proteins (sHSPs), HSP60, HSP70, HSP90, HSP100 (31). Mainly, HSP101 and sHSPs are found in maize. HSP101s and members of the ZmHSP20 family function primarily to inhibit irreversible protein denaturation, preserving protein integrity and assisting in the reactivation of aggregated protein. HSP70s play a dual role by remodelling misfolded proteins into their correct conformations and refolding newly synthesized polypeptides, especially during heat stress. Alongside HSP70s, HSP90s also aid in the proper folding and stabilization of nascent proteins, ensuring cellular functionality under stress. Moreover, HSPs are involved in the proteolytic breakdown of unstable or misfolded proteins, preventing cytotoxic accumulation and maintaining proteome homeostasis. They also enhance protein translation and translocation across cellular membranes, ensuring efficient intracellular protein trafficking. Importantly, HSPs safeguard the functioning of protein biosynthesis by stabilizing ribosomes and the translation machinery, thereby supporting continued growth and development under elevated temperatures (32). In maize, Nicotiana PK1 gene improves moisture stress resistance (33). Additionally, bacterial RNA chaperons were used in transgenic method to increase moisture stress tolerance in maize (34). Transgenic maize with higher ZmVPP1 expression restores drought (35). Previous researchers reported that over-expression of OsMYB55 activates stress-responsive genes and increases heat and drought tolerance (36). Transcription factors (TFs) play a pivotal role in regulating gene expression during heat stress, enabling plants to activate defence mechanisms at the molecular level. Among them, heat shock transcription factors (HSFs) are key regulators that activate the expression of heat shock proteins (HSPs), which maintain protein stability under stress. In maize, 31 HSFs have been identified and grouped into three classes: A, B and C. Class A HSFs, including ZmHsf1, ZmHsf4, ZmHsf5, ZmHsf6 and ZmHsf17, are primarily involved in transcriptional activation under heat stress. These TFs enhance thermotolerance by inducing protective genes like HSP70 and HSP101. Class B members such as ZmHsf3, ZmHsf11 and ZmHsf25 often function as co-regulators, fine-tuning the heat stress response by modulating expression levels of target genes. Other TF families like DREB, bZIP, WRKY and MYB are also reported to modulate abiotic stress responses in maize. For instance, ZmDREB2A is crucial for heat and drought tolerance, while ZmbZIP60 activates HSF genes and downstream chaperones. Collectively, these TFs coordinate signalling networks that reprogram cellular metabolism, promoting survival and adaptation under elevated temperatures. (37, 38)
Heat stress tolerance traits such as pollen viability and anthesis-silking interval (ASI) are governed by multiple genes or loci. Identifying heat-tolerance-associated QTLs is critical for developing high-yielding maize cultivars. Several QTLs influencing key reproductive traits like pollen production, grain filling and leaf senescence have been mapped. For instance, two grain yield-related QTLs have been recognized among the 11 reported for heat tolerance. Molecular markers linked to these QTLs have been successfully used in breeding programs. For example, former researchers identified QTLs associated with grain yield under stress and used them in hybrid development in tropical maize (39) . Previous researchers employed genomic prediction and marker-assisted selection (MAS) to develop stress https://plantsciencetoday.online
-resilient hybrids in sub-Saharan Africa (40). Similarly, the release of heat-tolerant hybrids like CHH 101 and CHH 105 in South Asia using QTL-based breeding strategies was reported earlier (41). Further demonstrated successful introgression of heat-tolerant QTLs into elite maize lines, improving pollen viability and grain yield under high temperatures (42). These studies highlight the utility of integrating molecular markers into breeding pipelines for the successful development of heat-resilient maize hybrids (Table 1).
functions and lead to the generation of numerous metabolomes within the broader metabolomics landscape (54). QTLs/genes involved in regulation of heat stress in maize is mentioned in Table 1.
Microarrays, which are tools used to assess the expression levels of thousands of genes simultaneously, have been instrumental in studying heat-related gene activity (55). Similarly, transcriptomes (the complete set of RNA transcripts) and phenomics (quantitative assessment of plant traits using imaging or sensors) provide detailed insight into plant responses at multiple stages. Therefore, omics-based methods offer promising avenues for identifying, selecting and developing maize genotypes better equipped to withstand rising temperatures (59).
Omics technology In the era of climate uncertainty, decoding the complex survival strategies of plants has become more important than ever. Modern science is now unlocking these secrets through Omics technologies, a powerful suite of tools that dives deep into the molecular orchestration of heat stress responses. These approaches provide an opportunity to explore translational, transcriptional and post-translational mechanisms, along with key signalling pathways that govern plant adaptation under extreme conditions (54). Omics helps identify the intricate links between alterations in plant genomes, micromes and proteomes during heat stress (55). In micromics studies, plants employ microRNAs to fine-tune gene expression post-transcriptionally, critical regulators in plant development and stress adaptation (56). Their role in ensuring transcriptome balance, cellular resilience and phenotypic plasticity offers immense potential for engineering heat-resilient cultivars (55). On the biochemical side, proteomes drive essential
By integrating phenotyping and crop modelling, researchers can now zero in on complex traits linked to stress adaptation (57). High-throughput phenotyping (phenomics), an emerging breeding strategy allows precise and large-scale trait screening. Although its high cost currently limits use to advanced breeding programs, recent advancements have significantly improved varietal development (6, 58).
Enhancing heat stress tolerance using genetic approaches To deal with the detrimental effects of severe temperature fluctuations, adopting diverse agronomic and breeding options as well as modern genomic technologies is a crucial step. Here, we can offer various ways to control the temperature extremes in maize cropping system. Agronomic practices Climate-smart agronomic practices are key strategies to combat the adverse effects of rising temperatures on maize yield. These
Table 1. QTLs/genes involved in the regulation of heat stress in maize QTLs name ZmHSF01
ZmHSF03 ZmHSF04 ZmHSF05 ZmHSF06 ZmHSF08 ZmHSF11 ZmHSF17 ZmHSF23 ZmHSF25 ZmHSF28 ZmDREB2A ZmMYB-R ZmbZIP60 Zm00001d043634 Zm00001d025343 ZmDHN13 ZmWRKY106 ZmERD3 ZmbZIP4 GRMZM2G377194 GRMZM2G060349 GRMZM2G122199 GRMZM2G026892 GRMZM2G148998 GRMZM2G115658 GRMZM2G537291 GRMZM2G324886 GRMZM2G436710 GRMZM2G094990 GRMZM2G178486 GRMZM5G806387 GRMZM2G148793
Related function in the previous study ZmHsf01 enhances thermotolerance via H3K9 promoter hyperacetylation in tropical and subtropical maize Heat stress response Overexpression boosts heat and salt stress tolerance Improves heat and drought tolerance Promotes thermo- and drought tolerance Suppresses ABA and stress-responsive genes under salt and drought stress Lowers heat stress tolerance Heat stress response particularly in Chinese maize varieties Contributes to heat stress response in sub-tropical maize lines Associated with heat stress response in thermotolerant tropical maize genotypes Enhances drought tolerance in both maize (a monocot) and Arabidopsis (a dicot) Crucial to withstand heat and drought during vegetative and reproductive stages. In tropical maize lines, ZmMYB-R is induced under abiotic stresses like heat, drought and cold. Activates ZmHSF01 and regulates many HSP genes in heat-tolerant sub-tropical maize genotypes Causes leaf burning and plant death at vegetative stage Causes leaf burning and plant death Enhances oxidative stress tolerance and positively regulates copper tolerance in transgenic yeast and tobacco Heat and drought tolerant in transgenic plants Heat and cold tolerance Regulates ABA accumulation and root development Thermotolerance Thermotolerance and increased seed set Thermotolerance Thermotolerance and increased seed set Heat tolerance and enhances grain yield at flowering time Heat tolerance at grain filling stage Heat tolerance, high grain yield Heat tolerance, high grain yield Heat tolerance Heat tolerance Cold tolerance Cold tolerance and better germination Cold tolerance, faster germination Plant Science Today, ISSN 2348-1900 (online)