Integrated morphological, physiological, and transcriptomic analyses reveal the survival strategies of alpine Rhododendron under chronic heat stress.

INTRODUCTION

Alpine Rhododendron species possess high ornamental value, but their sensitivity to prolonged high temperatures limits their application in subtropical regions.

METHODS

To elucidate the mechanisms underlying chronic heat tolerance, distinct from classical acute heat-shock responses, this study integrated phenotypic screening, physiological profiling, transcriptomics, and biochemical analysis of the glutathione system.

RESULTS

The heat-tolerant cultivar 'Gommer Waterer' maintained membrane integrity under 30-day chronic heat stress despite accumulating substantially elevated H₂O₂ levels, a dissociation consistent with preferential detoxification of lipid peroxidation products rather than broad-spectrum ROS scavenging. Comparative time-course transcriptomics revealed that the tolerant cultivar mounted a substantially larger and earlier transcriptional response than the heat-sensitive cultivar 'Fenjingling', with sustained enrichment of phenylpropanoid, lipid metabolism, and glutathione pathways. Weighted gene co-expression network analysis identified a key module significantly correlated with heat resilience traits and enriched in glutathione metabolism. Biochemical assays corroborated these network findings, with the tolerant cultivar showing higher constitutive GPX activity, a stress-induced surge in GST activity, and active glutathione redox cycling, whereas the sensitive cultivar displayed elevated GSH/GSSG ratios accompanied by transcriptional repression of recycling enzymes GR and DHAR, suggesting redox stagnation rather than active defense.

DISCUSSION: Collectively, these findings suggest that glutathione-mediated detoxification of lipid peroxidation products is associated with membrane protection under prolonged thermal stress in this species, with the Theta-class hub gene GSTT1 representing a candidate target for future functional validation and heat-tolerance breeding in woody ornamentals.