Spaceflight Disrupts Transcriptome Dynamics and Germination in Date Palm (Phoenix dactylifera) Seeds

Abstract

Spaceflight offers a unique setting for investigating plant stress responses and molecular pathways that enable adaptation to microgravity. Here, we examined the physiological and transcriptomic responses of date palm (Phoenix dactylifera L.) seeds maintained aboard the International Space Station (ISS) for six months. Germination assays revealed that space-exposed seeds from six cultivars failed to germinate, even after exogenous gibberellic acid and cytokinin treatments, whereas ground controls achieved 100% germination. Biochemical analyses indicated significant reductions in protein content, α-amylase activity, and proline levels, indicating impaired antioxidant capacity and reduced reserve mobilisation. Transcriptomic profiling of three representative cultivars (Lulu, Majdool, and Meselli) revealed extensive differential expression with Majdool exhibiting the strongest suppression. Downregulated genes were enriched in mitochondrial respiration, antioxidant defense, and auxin and ethylene signalling, whereas abscisic acid-related dormancy genes were upregulated. Additional disruptions included the suppression of DNA repair mechanisms, cytoskeletal organisation, and negative gravitropism regulators. The qRT-PCR validation of the selected genes confirmed these trends. Together, these results indicate that spaceflight seeds remain viable but enter a state of physiological stasis enforced by ABA dominance, impaired energy metabolism, oxidative imbalance, and disrupted growth orientation. To our knowledge, this is the first report on the long-term space exposure of a perennial fruit tree, providing new insights into seed biology under microgravity and highlighting critical challenges for future extraterrestrial agriculture.