Transcriptome and photosynthetic analyses provide new insight into the molecular mechanisms underlying heat stress tolerance in Rhododendron × pulchrum Sweet.

This article investigates the physiological and molecular responses of Rhododendron × pulchrum Sweet, an ornamental plant, to heat stress (HS) and subsequent recovery. The study demonstrates that HS at 40 °C/35 °C impairs photosystem II (PSII) activity and electron transport, while photosystem I (PSI) shows greater thermostability, with chlorophyll fluorescence kinetics revealing reversible damage after a recovery period. Transcriptome analysis identified significant down-regulation of genes encoding photosynthesis-antenna proteins (LHCb1, LHCb2, LHCb3) and carbon fixation-related enzymes during HS, alongside up-regulation of antioxidant-related genes (ascorbate peroxidase APX3, glutathione S-transferase GSTU8) involved in reactive oxygen species scavenging. Weighted gene co-expression network analysis (WGCNA) further pinpointed hub genes linked to photosynthetic efficiency and heat shock proteins (HSP70, HSP90) as key regulators in the heat stress response. These findings enhance understanding of the molecular mechanisms underlying heat tolerance in R. × pulchrum and provide candidate genes for breeding heat-resilient cultivars.