Heat Stress Physiology in C4 Crop Plants: Molecular Mechanisms, Omics Approaches and Strategies for Enhanced Thermotolerance

Rising global temperatures pose unprecedented challenges to agricultural productivity, with C4 crops including maize, sorghum, sugarcane, and pearl millet facing increasing heat stress despite their evolutionary adaptation to warm environments. This comprehensive review synthesizes current understanding of heat stress physiology in C4 plants, examining molecular mechanisms, omics approaches, and strategies for enhanced thermotolerance. Heat stress disrupts critical cellular processes including C4 photosynthesis, membrane stability, and protein homeostasis, with temperatures exceeding 35-40°C causing significant yield losses. C4 plants employ sophisticated defense mechanisms involving heat shock proteins (HSPs) and transcription factors (HSFs) that maintain protein quality. Key molecular components include Rubisco activase variants sustaining photosynthetic carbon fixation, photosystem II stability factors preventing photo inhibition, and antioxidant systems managing reactive oxygen species. Compatible solutes such as proline and glycine betaine provide osmotic adjustment, while membrane lipid remodeling maintains structural integrity. Recent omics technologies have revolutionized understanding of heat tolerance, revealing complex gene regulatory networks governing thermotolerance. Genomics studies identify quantitative trait loci associated with heat tolerance, while transcriptomics reveals coordinated gene expression changes. Proteomics and metabolomics uncover post-translational modifications and metabolic adjustments critical for survival under heat stress. Breeding programs increasingly incorporate molecular tools including marker-assisted selection, genomic selection, and gene editing to accelerate development of heat-tolerant varieties. Integration of multi-omics data with advanced phenotyping enables precision breeding for climate resilience. Climate projections indicate continued warming will challenge C4 crop productivity, making enhanced thermotolerance essential for food security through coordinated research combining fundamental mechanistic studies with applied breeding programs.