Analysis Of The Repetitive Elements In Wheat Group 7 Chromosomes

In higher plant,repetitive elements have great effect on genome complexity,gene expression and genome evolution.Common wheat occupied one of the most complex and large geneome,whose repetitive element is estimated to account for 80-90%.Systematical identification of the abuandance and composition of the repeat elements in wheat will provide the vital information for facilliting wheat genomic orgion,evolution and variation studies.In this study,we comparatively analyzed the abuandance and composition of the transposon elements of wheat at the chromosome level,with the case of group 7 chromosomes.The main results were obtained as follow:1.The length of 7AL,7AS,7BL,7BS,7DL,7DS was 252 Mb,198 Mb,259 Mb,257 Mb,206 Mb,222 Mb,209 Mb,separately,while of which 69.17%,65.47%,64.65%,70.64%,62.36%,62.78%was repetitive elements.About 80%of the repeat DNAs was RNA transposons,around 19%was DNA transposons,the remaining 1%was belong to tandem repeats or unknown clades.Among transposon elements(TEs),Gypsy occupied the most,followed by the Copia and the CACTA,which was consistent with the similar studies in monocots.Though Fatima,Jorge and Sabrina could respectively account for over 10%of the whole genome,there were a large number of low content families.7 of the 10 most abundant TE families were shared by the 7A,7B and 7D,named Angela?Jorge?Fatima?Romani?Sabrina?WHAM?Wilma.Some chromosome-special TE families were identified as Horace in 7B,Dario and E.Coli in 7D together with Spelt 1.2.The abundance,composition and variation of Stowaway-like MITEs were particularly analyzed at the chromosome level in wheat group 7 based on the survey sequences.In total,2,026 MITEs were identified.Of the 18 well-characterized MITE families,16,17 and 17 were found on 7A,7B and 7D,respectively.while 7A lacked Jason and Phoebus,7B lacked Jason and 7D missed Polyphemus.A total of 587,714 and 725 MITEs were found on 7A,7B and 7D,respectively.There are more MITEs present on 7D,compared to 7A and 7B,suggesting A and B sub-genome eliminated some repetitive elements during two hybridization processes.Interestingly,the nucleotide diversity for each MITE family was higher than previous studies,which may be related to the sequencing technology and MITE sequences screening standards.3.Furthermore,we developed 6 MITE primers based on the MITE conserved sequences,when validating in 30 hexaploid wheat and its closely relatives,all the primers could amplified fragments and 2 of them showed polymorphisms,which indicated that MITE primers could be used as molecular markers on Triticum population genetics and evolution study.This is the first systematics characterization of transposon elements in wheat on chromosome or chromosome arm level,as well as a special detection of the Stowaway-like MITEs.The research should be useful for the wheat genomics and genome evolution,the primers developed could also help to the population genetic diversity.