Regulation Of Gene Expression By Small RNA Durinig Hybridization And Polyploidization Between Brassica Juncea And B.oleracea

Distant hybridization and polyploidization are important methods to acquire germplasm resources with high quality,which are also the main impetus of speciation and evolution.In this study,we used triploid hybrid(Ho,genome ABC),hexaploid(So,genome AABBCC)and their parent lines tuber mustard(Brassica juncea),red cabbage(B.oleracea)as plant materials,and studied on the regulation of gene expression by small RNAs during the processes of hybridization,polyploidization and germplasm innovation.After analyzing and comparing the nutrient components,we clarified the advantages of nutritional quality traits in hexaploid.Then,by Digital Gene Expression Profile,differentially expressed genes were selected between So and Ho.Based on that,we elucidated the correlation between gene expression and predominant traits.Via small RNA-seq,we explored the regulation of small RNA on gene expression,which affected the predominant traits in hybrid and polyploid.Meanwhile,with hexaploid as the core germplasm,we synthesized new vegetable germplasms in Brassica.The main results were as follows:(1)The contents of soluble sugar and soluble protein of So were close to tuber mustard,but higher than red cabbage and Ho.The content of vitamin C in So was a little higher than Ho and the parents,while GS content of So had obvious advantages.The results indicated polyploidization may probably effect the flavor quality,insect resistance and plant defense.(2)Differentially expressed genes between progenies(Ho and So)and the paternal parent were 3389 and 3935,and 849 and 801 between progenies and the marternal parent,respectively.However,there were only 404 DEGs between So and Ho.This indicated that hybridization was the main reason resulted in gene expression changes,and progeny diverged markedly from B.oleracea,leading to the expression level dominance biased toward AB-genome.In addition,only a few genes were nonadditively expressed in progenies,and more than 70%of them were repressed,while the majority(about 85%)of the nonadditive repressed genes had a higher expression level in the paternal parent.Therefore,the transcriptome differences of the paternal lines were reconciled during hybridization and polyploidization,especially inhibited the expression of paternal genes.Furthermore,the predominant traits of GS content were related to the nonadditive activated expression of genes(MAM gene family)in hexploid.(3)Differential known miRNAs played a role in metabolism,biological regulation and stimulus response,however,the differential novel miRNAs were mainly enriched in the formation of leaf morphology,meristematic phase transformation and transcription factor activity regulation process.In addition,only a few known miRNAs were found expressed nonadditively in progenies,which were all nonadditive repressed,such as bra-miR156,bra-miR164 and bra-miR1885.They played important roles in regulating flowering time,leaf development and resistance to stress.The expression of siRNA in progenies was lower than that in the parents,which might lead to the activation of transposon,and it might influence the new phenotype in progeny.Compared with the siRNA tags between progeny and the parents,the number of expressed siRNAs were decreased significantly in hybridization,but eased during polyploidization,which indicated siRNA indeed contributes to the genome stability.(4)New germplasms of genome AABBC and AABC were successfully obtained from the crossing combinations between So and Brassica juncea,B.rapa respectively.Compared with the parents,AABBC had obvious advantages in disease resistance,and AABC has the potential to be a fresh vegetable germplasm.