Studies Of Arabidopsis Importin Protein And RNA Topoisomerase In RNA Metabolism

The process of RNA metabolism is very important for the growth and development of organisms.However,there are actually many regulatory processes of RNA metabolism that we don't know.Here,we study the three pathways of RNA metabolism: RNA degradation,post-transcriptional gene silencing,and transcriptional gene silencing.Attempt to find other regulatory factors in these three RNA metabolism pathways in Arabidopsis.The degradation of mRNA is necessary for the quantity and quality control of mRNA.The classic view is that mRNA only degrades after complete protein translation,but recent studies have shown that mRNA may also degrade while translating in plant.Eukaryotic mRNA can be degraded in two directions: 5'-3 'degradation,RNA decay by XRNs complex is mediated by several complex exo-or endo-ribonuclease;3'-5' Degradation,exosome dimer defined hexamer ring.Exosomes require different cofactors for processing and degradation.For example,MTR4 in nucleolus,HUA ENHANCER2(HEN2)in nucleoplasm and SUPERKILLER(SKI)complex in cytoplasm.We found that the sic1-1 mutant of the Arabidopsis importin protein SIC1 can be rescued by the ski2-2 and ski7-1 mutants of the SKIs complex in the 3'-5 'pathway.This may imply that SIC1 can act as a regulator of RNA degradation in the 3'-5 'pathway.In the case of abnormal RNA degradation pathways,the accumulation of abnormal transcripts will initiate post-transcriptional gene silencing.It has been demonstrated in Arabidopsis that both 5'-3 'and 3'-5' cytosolic RNA degradation pathways can act as repressors of transgenes and endogenous PTGS.Post-transcriptional gene silencing is triggered by the synthesis of double-stranded RNA by RDR6 / SGS3,which is then cleaved into 22-nt siRNA and 21-nt siRNA by DCL2 and DCL4,respectively.siRNA can loading to the Argonaute(AGO)silencing complex,which targets homologous RNA precipitation and/or translation inhibition.RNA polymerase can generate secondary small interfering RNA(siRNA)molecules after the main siRNA is targeted,thereby amplifying the role of PTGS.In our study,we found that only the dcl2-1 mutant of PTGS can rescued the phenotype of the sic1-1 mutant.We speculate that SIC1 may participate in the PTGS process only through DCL2 in the PTGS pathway,but the specific mechanism needs to be further explored.Transcriptional gene silencing(TGS)is mediated by 24-nt siRNA generated by DCL3 cleavage,and is usually linked to the production of RDR2,which produced by the transposon and repeated RNA directed DNA methylation(Rd DM).Its function also needs loading to AGO4 or AGO9.Interestingly,we found that the rdr2-2,dcl3-1,ago4-1,and ago9-2 mutants of this pathway can rescue sic1-1 mutant,which shows that SIC1 acts as a regulator of the entire TGS pathway,possiblely.In addition,we also studied the candidate RNA topoisomerase AtTop3? in Arabidopsis,unfortunately we found that the double mutants of Attop3? mutant cross with dcl4-2,ski2-2 mutant of PTGS pathway and ein5-1 mutant of RNA degradation pathway shows no difference phenotype compared to WT.In summary,we found that SIC1 may be involved in the regulation of RNA metabolism,RNA degradation,PTGS,and TGS through classical genetic methods,but the specific mechanism needs to be further explored.