Genetic mapping and transcriptomic profiling reveal key regulators for heat tolerance during meiosis in wheat

Heat stress seriously limits global wheat ( Triticum aestivum L.) productivity but the impact of heat during meiosis remains relatively unexplored. This study aimed to identify genomic regions and candidate genes for heat tolerance during meiosis in the main stem spikes of two F₂ populations derived from the crosses of heat-sensitive (HS) wheat cultivar Gladius by heat-tolerant (HT) cultivars Vixen and Hellfire. A total of 13 and five QTL were identified in Gladius_HS × Vixen_HT (population-GV) and Gladius_HS × Hellfire_HT (population-GH), respectively. Three QTL in each population shared a common marker (2276320) on chromosome 5A which hosts a hotspot for traits associated with growth and grain yield under heat stress. Genome-wide association analysis in population-GV and population-GH further supported these QTL for heat tolerance. Candidate genes within five major QTL regions ( QBM.uwa.5A, QTNT.uwa.5A, QDTA.uwa.5A.2, QDTA.uwa.5A, QGN.uwa.5A and QGY.uwa.5A) were associated with regulation of meiotic cell cycle progression ( TraesCS5A03G0891600 ), heat shock response ( TraesCS5A03G0895300 ), temperature stimulus and carbohydrate metabolism TraesCS5A03G0943300 ), transcription regulation ( TraesCS3B03G1331000, TraesCS3B03G1329000 and TraesCS3B03G1328500 ), and oxidative stress response ( TraesCS5A03G0950600 ). RNA transcriptomic profiling was conducted on main stem spike tissues from Gladius_HS, Vixen_HT and F_2:3 families in population-GV under heat and control treatments during meiosis. A higher number of differentially expressed genes (DEGs) were upregulated under heat stress in Vixen_HT than in Gladius_HS. Heat tolerance was associated with upregulation of transcription factors (TFs) regulating heat shock proteins HSP70 and HSP40, ATPase superfamily, lipases, ubiquitin-related proteins, and cytochrome P450s. Gene pathway analysis revealed enrichment in protein metabolic processes, membrane targeting, asparagine synthase activity, and secondary metabolite biosynthesis. A set of 44 DEGs differentiated Vixen_HT and heat-tolerant F_2:3 families from Gladius_HS and heat-sensitive F_2:3 families in population-GV. Several DEGs were validated in qRT-PCR analysis. Heat tolerance during meiosis was associated with the upregulation of TFs that establish cellular homeostasis and meet the high energy demands of cells under heat stress. These findings establish a strong genetic and molecular foundation for breeding wheat cultivars tolerant to heat stress during meiosis.