Synthetic allopolyploidy unveils hybridization-driven transcriptional reprogramming underlying thermal adaptation in Cucumis

Both heterosis (hybrid vigor) resulting from hybridization and genetic plasticity conferred by whole-genome duplication (WGD) are recognized as drivers of evolutionary success and ecological adaptation in plants. Allopolyploids, which combine both hybridization and WGD, are widespread in both natural and agricultural settings and often exhibit superior performance. However, the relative contributions of these two elements to the success of allopolyploids remain poorly understood. Here, we employed an experimentally reconstructed allotetraploid Cucumis species (C. × hytivus, 2n = 4x = 38) and its diploid interspecific hybrid progenitor (allodiploid, 2n = 2x = 19) to decouple and investigate the distinct and combined contributions of hybridization and whole-genome doubling to immediate genetic and phenotypic consequences of allopolyploid formation under environmental stress. Both C. × hytivus and the allodiploid exhibited superior heat tolerance compared with the parental species with significantly higher semi-lethal temperature and enhanced physiological acclimation capacity. While the allodiploid and allotetraploid retain transcriptomic features where differences persist (e.g., WGCNA modules), comparative analysis of the 15,680 homoeologous gene pairs in the allodiploid and allotetraploid under heat stress (45°C) versus control conditions (28°C) revealed conserved heat-responsive transcriptional plasticity, suggesting that enhanced thermotolerance in C. × hytivus is presented as consequences arising dominantly after interspecific hybridization. This study provides mechanistic insights into allopolyploid adaptation through experimental reconstruction of allopolyploid genomes, demonstrating that hybridization initiates key transcriptional and physiological advantages under stress, subsequent WGD stabilizes these adaptations and contributes to the full phenotypic realization. This work decouples the roles of interspecific hybridization and WGD and proposes a synthetic biology approach for developing climate-resilient crops.