Identification of ascorbate peroxidase family genes reveals expression of TkAPX250a confers heat stress tolerance in Taraxacum kok-saghyz.

Ascorbate peroxidase (APX) enzymes are pivotal in scavenging reactive oxygen species (ROS) and maintaining redox homeostasis in plants, a function critical for survival under abiotic stress conditions. To investigate this key enzyme system in the rubber-producing dandelion Taraxacum kok-saghyz (Tk)-an emerging model for sustainable rubber production-we conducted a genome-wide analysis of its APX genes. We identified seven TkAPX genes, whose predicted subcellular localizations include the cytoplasm, plasma membrane, and chloroplasts. Promoter analysis revealed an abundance of stress-responsive motifs, supporting their potential role in stress adaptation. By integrating time-course qPCR of the TkAPX family under heat stress with transcriptome-wide expression profiling across tissues, we identified TkAPX250a as a pivotal candidate. This gene showed a remarkable ∼ 20-fold increase in transcript levels in subsequent transgenic lines compared to wild-type controls, confirming highly efficient transgene expression without silencing. Under thermal stress, these transgenic lines exhibited reduced ROS accumulation and membrane lipid peroxidation while maintaining higher chlorophyll content and biomass, demonstrating that TkAPX250a coordinately enhances thermotolerance and photosynthetic stability. Mechanistically, TkAPX250a overexpression not only enhanced APX activity and lowered H2O2 accumulation but also synergistically upregulated the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Time-resolved assays under heat stress further delineated a stratified antioxidant hierarchy within this coordinated response, with SOD and CAT acting as core responders. These findings establish TkAPX250a as a central genetic regulator in abiotic stress adaptation and provide a molecular basis for breeding stressresilient rubber crops, addressing a critical need in agriculture under changing climate conditions.