The Trx-Prx redox pathway and PGR5/PGRL1-dependent cyclic electron transfer play key regulatory roles in poplar drought stress.

Understanding drought resistance mechanisms is crucial for breeding poplar species suited to arid and semiarid regions. This study explored the drought responses of three newly developed 'Zhongxiong' series poplars using integrated transcriptomic and physiological analyses. Under drought stress, poplar leaves showed significant changes in differentially expressed genes linked to photosynthesis-related pathways, including photosynthesis-antenna proteins and carbon fixation, indicating impaired photosynthetic function and carbon assimilation. Additionally, drought stress triggered oxidative damage through increased reactive oxygen species production, leading to malondialdehyde accumulation. Weighted gene co-expression network analysis revealed that differentially expressed genes closely associated with physiological responses were enriched in cell redox homeostasis pathways, specifically the thioredoxin-peroxiredoxin pathway. Key genes in this pathway and in cyclic electron flow, such as PGR5-L1A, were downregulated, suggesting compromised reactive oxygen species scavenging and photoprotection under drought stress. Notably, ZX4 poplar exhibited higher drought tolerance, maintaining stronger activity in cyclic electron flow and the thioredoxin-peroxiredoxin pathway compared with ZX3 and ZX5. Genes like PGR5-L1A, 2-Cys Prx BAS1, PrxQ and TPX are promising candidates for enhancing drought resistance in poplars through genetic improvement, with potential applications for developing resilient forestry varieties.