Differential Expression Mechanism Of Paralogous Genes In The Hybrids Of B.rapa And B.oleracea

Brassica rapa,Brassica oleracea and its distant hybridization are important resources of vegetable and oil crops.Along with the fast development of sequencing and assemblying,the whole genome sequencing and gene annotation of B.rapa and B.oleracea were completed,which is important to study of biology Brassica crops.Paralogous gene means in one genome,the gene pairs are from duplication of ancestor genes.A set of paralogous genes were generated from distant hybridization.Now,very little has been learned about the genetic mechanism on the expression regulation of paralogous genes after hybridizing or tetraploidization.Studies have shown that paralogous genes retain hight level of DNA sequences similarity,however their expression levels are differentiated,and the relevant mechanisms are still unclear.Prsvious reports show that epigenetic modification may play an important role in this process.In this study,the relationship of epigenetic modification and differential expression of paralogous gene in the distant hybrids of B.rapa and B.oleracea has been analyzed.We chose B.rapa variety Chiifu and B.oleracea variety JZS to do distant hybridization.After the embryo rescue technique being used to obtain the allodiploid(named AD1),the allotetraploid(named AT1)of AD1 was obtained by the method of colchicine doubling.Then determined paralogous gene pairs,and use the "two-fold" principle to obtain paralogous genes of differential expression.Finally,we focused on the TE,24-nt s RNA and three types of DNA methylation(Cp G,CHG and CHH)and analyzed the potential relationships between these genetic modification and paralogous gene's expression.The main results are as follows:1.In the study of transposons distribution of B.rapa,B.oleracea,their hybridization AD1 and AT1,senerally gene expression was found to be negatively related to the density of transposons,and regions of gene upstream 1 kb to downstream 1 kb are most relate to gene expression.So we defined 1 kb to transcription start site and 1 kb to transcription termination site sa important regions in following analysis.2.In the study of paralogous gene,transposons density in gene upstream and downstream regions are unrelated to its expression,whereas in gene regions,transposons density and paralogous gene expression has negative correlation.3.We found that there's no relation between 24-nt s RNA targenting in upstream and downstream regions or gene regions and the expression level of paralogous gene.In further analysis of the 24-nt s RNA targeted transposons,we also found that it hasn't obvious relationship to the differential expression of paralogous genes.4.In upstream and downstream regions of genes,three types' DNA methylation(Cp G,CHG and CHH)level and the level of transposons methylation are all independent to the differential gene expression of paralogous genes.While in genic region,the lower the expression level of one paralogous gene,the higher the methylation levels of CHG and CHH types were found.In the research on DNA methylation targeted transposons,genic CHG and CHH type transposon methylation and paralogous gene differential expression are negatively correlated.In general,in upstream and downstream regions of paralogous genes which from the hybridization of Brassica rapa and Brassica oleracea,there is no relationship between differencial gene expression and factors as transposons,24-nt s RNA,24-nt s RNA target transposons,DNA methylation,DNA methylation of transposons.And in gene region of paralogous genes,there is negative correlation between differential expression of paralogous gene and either of transposons density,CHG methylation,CHH methylation,CHG methylation of transposons,CHH methylation of transposons and.