Structural And Evolutionary Analysis Of MULEs From Setaria And Oryza Species

Mutator transposon was first discovered by Robertson in maize.The Mutator(Mm) system has been described as the most active and mutagenic plant transposon.Mu -like elements(MULEs) are of different variation in other plants.The active Mutator transposon is only discovered in Decrease in DNA Methylation(DDM1 ) mutant of Arabidopsis and in Fusarium oxysporum.Thus,learning the state of Mutator transposon in other species besides maize and turning it into an active transposon will help us to recognize the origin and evolution history of transposon,and understand its role in genome evolution,gene regulation and gene expression,and use the transposon for tagging gene and genomic analysis.Based on the terminal inverted repeats(TIR) of Os493,primer TIR1 was designed to clone MULEs in 12 different species of Setaria.A 3.6kb fragment was obtained from all of the species used.And MULEs cloned from Setaria samples are of terminal inverted repeats in their flanking sequence.Transposase MURA binding site(MBS) was discovered in TIRs. D-D-E structure,which is related with transposon transpose activity,and a 25 amino acids signature sequenceD-x(3)-G-[LIVMF]-x(6)-[STAV]-[LIVMFYW]-[PT]-x-[STAV]-x(2)-[QR]-x-C-x(2)-H were revealed too.Plant Mutator transposon zinc finger structure Znf-pmz and DNA binding domain CX₂CX₄HX₄(_或6)C(X represent any amino acids) were also discovered in the C terminal of MULEs from Setaria samples.But almost all of these structures are of different degrees of variation,which indicates that they have no transposon activity at the present state.Using primer sxdl and sxd2,PCR were cloned from materials from Oryza and Setaria, and lots of 600bp fragment were obtained,which were of high similarity.This section was the most conserved of Mutator transposon,whose homology with MUDA was 53%-56%.But there are of terminal codon and frame shift,indicating that all of the MULEs is not active any more.From the constructed phylogenetic tree using these sequences,we known that they were divided into three major groups,including Classâ… ,Classâ…¡and Classâ…¢.The sequences grouped into Classâ… and Classâ…¡were all from Oryza.However,Classâ…¢is involved in 8 sequences from Oryza and all sequence from Setaria.The 8 sequences from Oryza is grouped with all of the sequence from Setaria,and 8 species from AA,BB,BBCC,CCDD,GG genomes,which shows that Mu transposon distribution is not continuous in Oryza.This phenomenon is explained by horizontal gene transfer between Oryza and Setaria.And there are a large number of high similarity sequences in Oryza and Setaria,demonstrating that massive horizontal gene transfer of MULEs transposon between Oryza and Setaria,and selection analysis also proved this point of view.