Transaldolase PagTAL1 modulates ROS homeostasis to improve heat stress tolerance in Populus

Global warming-induced high-temperature stress significantly impairs plant growth and development. As a key enzyme in the pentose phosphate pathway (PPP), transaldolase (TAL) has been found to play a significant role in plant growth regulation. However, its function in poplar under high-temperature stress remains poorly understood. In this study, we identified and characterized a poplar transaldolase gene, PagTAL1, which localizes to chloroplasts. Tissue-specific expression analysis revealed that the PagTAL1 exhibits differential expression patterns, with the lowest transcript levels in young leaves and the highest in young stems. Metabolomic profiling revealed PagTAL1 reprograms metabolism, with significant enrichment in the ascorbate and aldarate metabolism pathway, which contribute to reactive oxygen species (ROS) scavenging. Phenotypic analysis under 40 °C stress conditions revealed that the PagTAL1-overexpressing plants exhibited enhanced thermotolerance, whereas CRISPR/Cas9-mediated knockout mutants showed increased sensitivity to high-temperature stress. Further physiological analyses demonstrated that PagTAL1 mitigates high-temperature stress by ROS scavenging capacity. Furthermore, we identified PagMYB94, a heat-inducible transcription factor that directly activates PagTAL1 expression, as demonstrated by dual-luciferase assays. These findings not only offer new insights into the molecular mechanisms of thermotolerance regulation but also provide PagTAL1 as a promising candidate gene for engineering heat-resistant poplar cultivars.