Rocket Science: The Effect of Spaceflight on Germination Physiology, Ageing, and Transcriptome of Eruca sativa Seeds

In the 'Rocket Science' project, storage of Eruca sativa (salad rocket) seeds for six months on board the International Space Station resulted in delayed seedling establishment. Here we investigated the physiological and molecular mechanisms underpinning the spaceflight effects on dry seeds. We found that 'Space' seed germination vigor was reduced, and ageing sensitivity increased, but the spaceflight did not compromise seed viability and the development of normal seedlings. Comparative analysis of the transcriptomes (using RNAseq) in dry seeds and upon controlled artificial ageing treatment (CAAT) revealed differentially expressed genes (DEGs) associated with spaceflight and ageing. DEG categories enriched by spaceflight and CAAT included transcription and translation with reduced transcript abundances for 40S and 60S ribosomal subunit genes. Among the 'spaceflight-up' DEGs were heat shock proteins (HSPs), DNAJ-related chaperones, a heat shock factor (HSFA7a-like), and components of several DNA repair pathways (e.g., ATM, DNA ligase 1). The 'response to radiation' category was especially enriched in 'spaceflight-up' DEGs including HSPs, catalases, and the transcription factor HY5. The major finding from the physiological and transcriptome analysis is that spaceflight causes vigor loss and partial ageing during air-dry seed storage, for which space environmental factors and consequences for seed storage during spaceflights are discussed.