Effects Of Space Environment On The Expression Of Different Repair Genes For DNA Damage In Arabidopsis Thaliana

In space environment,microgravity and space radiation are the two most important stressors that cause biological effects.In order to explore the effects of plant gravitational response mechanism on space environment-induced DNA damage repair,we used the Shijian-10 recoverable satellite(SJ-10)to conduct 303-hour seed loading of Arabidopsis thaliana seeds with different gravitation responses.After returning,420 days of ground preservation were carried out.And then,from the perspective of phenotypic,physiological and molecular levels,we investigated the effects of gravitation and gravitropism on repair gene expressions for space environment-induced DNA damage in plant Arabidopsis thaliana at seedling growth,vegetative growth transitioning to reproductive growth(hereinafter referred to as vegetative growth).In this study,the seeds of wild-type and two mutants with defects in the gravitational response mechanism(e.g.,pin2,pgm-1)were divided into the ground control groups and spaceflight groups.And then,these seeds were cultivated in the climatic chamber.The seed vigor,root length and root apical deflection angle were measured at the seedling stage(cultivation for 7 days);and the biomass and Fv/Fm were also determined at the vegetative growth stage(cultivation for 28 days before bolting).And the genes expression of the biomakers in the non-homologous end joining,homologous recombination,base excision and nucleotide excision repair pathways,such as Ku70,RAD51,OGGI and XPD,were detected for both the above stages in Arabidopsis thaliana,respectively.Our results showed that no significant changes were found in the germination potential and root apical deflection angle after spaceflight.In addition,the root lengths were significantly inhibited in wild-type and pin2,pgm-1 mutants after the spaceflight,while the germination rate in pgm-1 mutant as well as the biomass and Fv/Fm in pin2 mutant were significantly increased after the spaceflight.Furthermore,at the seedling stage,the gene expression of the XPD was significantly up-regulated in the wild-type A.thaliana,and the gene expressions of the Rad51,OGGI,XPD in pin2 mutant and the Ku70,OGGI in pgm-1 mutant were also significantly up-regulated after the spaceflight.At the vegetative growth stage,no significant differences of the four damage repair genes were observered in wild-type,while the expressions of Rad51,OGG1 and XPD in pin2 mutant were up-regulated,and the expression of Rad51 in pgm-1 mutant was significantly up-regulated.In summary,the space stress still exists in the seeds of A.thaliana after 420 days back from spaceflight,which mainly indicates that the root lengths were reduced after spaceflight.And the stress effect is more obvious in the mutants without gravity signal transduction.It is speculated that the mutation may increase the sensitivity to the space environment.The expressions of DNA damage repair genes were different between the two developmental stages after the spaceflight.Moreover,the mutation of gravitropic signal transmission gene pin2 affects the sustained genes expression of HR,BER and NER pathways from seedling stage to vegetative stage;the mutation of gravity perception gene pgm-1 affects the genes expression of NHEJ and BER pathways in the seedling stage,while the HR mechanism response was initiated at vegetative stage.