Potential evidence for transgenerational epigenetic memory in Arabidopsis thaliana following spaceflight.

Plants grown in spaceflight exhibited differential methylation responses and this is important because plants are sessile, they are constantly exposed to a variety of environmental pressures and respond to them in many ways. We previously showed that the Arabidopsis genome exhibited lower methylation level after spaceflight for 60 h in orbit. Here, using the offspring of the seedlings grown in microgravity environment in the SJ-10 satellite for 11 days and returned to Earth, we systematically studied the potential effects of spaceflight on DNA methylation, transcriptome, and phenotype in the offspring. Whole-genome methylation analysis in the first generation of offspring (F) showed that, although there was no significant difference in methylation level as had previously been observed in the parent plants, some residual imprints of DNA methylation differences were detected. Combined DNA methylation and RNA-sequencing analysis indicated that expression of many pathways, such as the abscisic acid-activated pathway, protein phosphorylation, and nitrate signaling pathway, etc. were enriched in the F population. As some phenotypic differences still existed in the F generation, it was suggested that these epigenetic DNA methylation modifications were partially retained, resulting in phenotypic differences in the offspring. Furthermore, some of the spaceflight-induced heritable differentially methylated regions (DMRs) were retained. Changes in epigenetic modifications caused by spaceflight affected the growth of two future seed generations. Altogether, our research is helpful in better understanding the adaptation mechanism of plants to the spaceflight environment.