| Epigenetic mechanisms are involved in plant growth and development and the regulation of stress resistance.Space radiation and microgravity are two essential stress factors in space environment,and their interactions in space biological effects have always been the focus of research.In previous studies,model organisms such as Caenorhabditis elegant and Arabidopsis thaliana(A.thaliana)were treated with spaceflight and ground simulation.The results showed that the expressions of functional genes related to DNA damage response pathway were affected by the synergistic effect of radiation and microgravity,as well as the sensitivity of organisms to gravity and radiation.However,it is not clear how epigenetic mechanisms are involved in this.To further study the regulation of epigenetic mechanism in radiation and microgravity effects,the seeds of A.thaliana(wild-type,gravity signal transduction-deficient mutant(pin2),and radiation-sensitive:mutant(ttgla))were carried on the Shijian-10 satellite for 303 hours.After returning,1062 days 9f ground preservation were carried out(to observe the chronic effects caused by spaceflight).The seeds ofA.thaliana were planted,and the growth and development characters of A.thaliana seeds were observed.Methylation sequencing and RNA sequencing of the genome of leaves developed to vegetative growth stage were carried out by high-throughput sequencing technique.The results showed that the germination potential,germination rate,root length,root tip deflection angle,and Fv/FM of the three Arabidopsis space groups had no significant changes compared with the control group.The results of the study on the whole-genome methylation level showed that after spaceflight,the CHG and CHH methylation levels of the wild-type increased by 1.2%and 1.8%,respectively,while the CG methylation level decreased by 1.1%.In pin2 mutant,both CG and CHG increased by 0.7%,and CHH decreased by 1.2%.In ttg1a mutant,CG and CHG increased by 3.0%and 2.1%,respectively,and CHH decreased by 1.9%.It indicated that the genome methylation patterns of gravity signal transduction-deficient mutant and radiation-sensitive mutant were different from wild-type after spaceflight.Meanwhile,demethylation induced by spaceflight in centromeric regions of wild-type(CG sequence)and ttg1a mutant(CHH sequence),suggesting that the space environment may induce genomic instability.Analysis of the number of differentially methylated regions(DMR)and methylation modification patterns showed that in the CG sequence of promoter and exon regions of wild-type and pin2 mutant were more hypomethylation(hypo DMRs)regions than hypermethylation regions(hyper DMRs),but the opposite was found in ttg1a mutant.There were 1248 DMR genes in wild-type,919 DMR genes in pin2 mutant,and 1135 DMR genes in ttg1a mutant.The proportion of hypermethylation and hypomethylation of wild-type,pin2 and ttgla mutants DMR consistent with the expression of corresponding genes in their transcriptome was 52.82%,47.77%,and 48.80%,respectively.This suggested that when the gravity signal transduction and stress resistance of A.thaliana decreased,the methylation pattern of A.thaliana changed and the number of genes regulated by methylation decreased.The biological function enrichment analysis of DMR genes of wild-type,pint mutant,and ttg1a mutant showed that components related to mitochondria(cell components)were significantly enriched,and the DMR genes were mainly involved in the oxidative phosphorylation pathway.Since the endogenous ROS is mainly derived from the oxidative phosphorylation process in the mitochondria,it can be speculated that the production of endogenous ROS was still induced after 1062 days back from spaceflight.Compared with the wild-type,the DMR genes of the pin2 and ttgla mutants are also involved in the functions and processes related to energy metabolism,indicating that the effects of spaceflight on the molecular function and biological processes of pin2 and ttg1a mutants are different from those of the wild-type.In summary,these results indicated that the sensitivity of organisms to radiation and microgravity stress affects the epigenetic mechanism involved in the synergistic biological effects of space radiation and microgravity. |
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