Mechanism Of Dose-biological Effects Induced By Heavy Ion Radiation In Rice

Unlike high-dose heavy ion radiation(HIR),the biological effect induced by low-dose HIR has no dose-dependent effect.The biological effects to response stress in low-and high-dose HIR groups may be induced by different mechanisms.Lots of research showed that epigenetic which involved in resistance to stress changed by both low-and high-dose HIR.However,the relationship between these changes and dose-biological effects remains unclear.It is a great help to understand the mechanism of biological effects of different doses HIR on plant seeds by investigating the changes of epigenetic,including RNA,protein expression and the methylation profiles,especially the gene expression of transcription factors(TFs),transposable elements(TEs)and DNA methyltransferase.In this paper,with Two-dimensional electrophoresis and methylation-sensitive amplified polymorphism technology,the results showed the phenotype,changed proteome profiles and DNA methylation of rice at tillering stage after seeds exposure to ground-based carbon radiation with different cumulative doses at 0,0.01,0.02,0.1,0.2,1,2,5,and 20 Gy(12C6+;energy,165 MeV/u;mean linear energy transfer,30 keV/?m).Two representative groups of low-and high-dose HIR were selected to further analyze the characteristics at three-leaf stage of rice after radiation treatment and compare the dynamic changes at different development stages.The high-throughput sequencing results showed the differences of epigenome,proteome and transcriptome between low-and high-dose HIR of rice at nutritional growth stage,especially the TEs,TFs and DNA methyltransferase,as well as the genes and proteins related energy metabolism and stress resistance.This paper revealed the role of DNA methylation involved in responding to radiation stress of dry seeds induced by low-and high-doses HIR at nutrition and reproductive stage,respectively.Our results are as follows:(1)The PCA results of differentially expressed proteins of rice at tillering stage showed that 1-2 Gy was the boundary of low-and high-dose HIR.The results showed that the protein expression profile in low-dose HIR groups was closer to the control group,while the expression patterns in high-dose HIR groups were significantly different.The function of changed proteins and DNA methylation variant genes showed that the metabolism process was affected by both low-and high-dose HIR,however,the processes of location or transfer and response to stress were changed in high-dose groups.(2)The result of overall relative cytosine methylation level showed that the type of hypo-methylation was higher than hyper-methylation on CG and CHH site caused by low-and high-dose HIR at vegetative growth stage.At tillering stage,the type of hypo-methylation was still higher than hyper-methylation on CHH site,while it was reverse on CG site caused by low-dose HIR.It suggested that the changes of DNA methylation induced by low-and high-dose HIR in rice seeds were dynamic changes with development,while the methylation at CG sites in low-dose HIR groups was recovered at tillering stage.(3)The transcriptome results of rice at vegetative growth stage showed that the DCL which cut off RNA into 24nt siRNA in RNA-directed DNA methylation pathway decreased expression,AG03 which interacts with RNA-RNA or RNA-DNA also decreased expression after radiation.Meanwhile,MET1 which catalyzes de novo and maintain methylation on CG site increased expression,however,the CMT3 which maintain methylation on CNG site decreased expression.The overall relative cytosine methylation level might be effected by these expression decreased DNA methyltransferase.(4)The rice TFs expression was different between low-and high-dose HIR in vegetative growth stage,which was more decreased in low-dose HIR group.C2C2(Zn)DOF,C3H zinc finger family,MYB-related,NAC domain,AtSR,Aux/IAA,GeBP lik and SET-domain were changed only in low-dose HIR group,while TCP and CCAAT box binding factor family were changed only in high-dose HIR group.It indicated that the TFs related energy metabolism decreased expression by low-dose HIR,whlie the TFs related lip metabolism increased expression by high-dose HIR.We speculated that low-and high-dose HIR might active different TFs to regulate target genes expression.(5)In low-dose HIR group,the down-expression nearby genes of DNA TEs were involved in proteins phosphorylation,and the ones of LTR TEs were related to redox reaction and stress response.While in high-dose HIR group,the ones of LTR TEs played part in proteins phosphorylation,redox reaction and transcriptional regulation,the up-expression nearby genes of DNA TEs were involved in redox reaction,and ones of LTR TEs were stress response and transcriptional regulation.The result showed that to response radiation stress in vegetative growth stage rice,the nearby genes of activity TEs decreased expression by low-dose HIR,while increased expression by high-dose HIR.