Heat stress-induced meiotic restitution and tissue-specific gene responses in the sterile Lilium OT Hybrid ‘Yelloween’

• Heat stress induced tissue-specific expression of HSPs, HSFs, APXs, PR10, and LIM15. • Anthers showed rapid activation of HSP17.6, HsfA2, APX2, PR10, and LIM15. • HSP70 was highly upregulated in leaves and moderately upregulated in anthers. • Heat exposure induced 18.85 % 2n-pollen (40 °C, 6 h), overcoming sterility barriers. • LIM15 upregulation suggests its role in stabilizing meiosis under stress. Heat stress poses significant challenges to plant reproduction by disrupting critical cellular processes and meiotic stability. This study investigates the molecular and cytological responses to heat stress in the sterile Lilium interspecific hybrid ‘Yelloween’. Quantitative Reverse Transcription PCR analysis revealed tissue-specific expression patterns of heat shock proteins (HSP17.6, HSP70), heat shock transcription factors (HsfA2 and HsfA4), antioxidant enzymes (APX1 and APX2), a pathogenesis-related gene (PR10), and the meiosis-specific gene LIM15 (DMC1 homolog) in leaves and anthers. Anthers exhibited rapid and robust activation of HSP17.6, HsfA2, APX2, PR10, and LIM15, whereas leaves demonstrated sustained upregulation of HSP70, highlighting distinct physiological priorities under stress. Cytological observations revealed heat-induced meiotic abnormalities, including lagging chromosomes and micronuclei, which correlated with the formation of unreduced gametes. Notably, LIM15 was significantly upregulated in anthers during heat stress, suggesting its role in stabilizing meiotic processes and facilitating crossover events. The production of 2n-pollen reached 18.85 % after prolonged heat exposure (6 h at 40 °C), underscoring the potential of heat-induced meiotic restitution in overcoming sterility barriers. These findings provide insights into the molecular pathways that regulate heat stress responses and their implications for breeding climate-resilient ornamental hybrids. Integrating molecular and cytological approaches enhances our understanding of stress-induced reproductive adaptations and their applications in crop improvement.