Study On The Expression Patterns Of Partial Homologs Of Hybrids Between Megalobrama Amblycephala And Culter Alburnus

Distant hybridization makes the interspecific genomes merge rapidly.The combination of heterologous genomes from different species may result in differences in the homologous genes expression of hybrid progenies,and it is considered as one of the main reasons for heterosis.The bisexual fertile allodiploid reciprocal hybrid lineages,BT?F₁^F₅?and TB?F₁^F₃?were obtained in our laboratory from distant hybridization between blunt snout bream?Megalobrama amblycephala,BSB,2n=48?and topmouth culter?Culter alburnus,TC,2n=48?,both of which belong to different genera.In this study,the expression patterns?including expression level dominance,expression bias,gene silencing and genomic imprinting?of homologous genes were analyzed based on the expression profiles of the liver transcriptome of BSB,TC and their hybrid progenies.The expression bias of homologous genes at different developmental stages and in different tissues was explored by quantitative real time polymerase chain reaction?qRT-PCR?.Besides,the nucleolar dominance in the fifth generation of hybrid progenies of BT was studied by sequencing technology.The main research contents of this paper are as following:1.Analysis on the expression patterns of homologous genes in liver expression profiles:The expression differences of homologous genes were identified by the number of SNPs?more than 3?.Total 3191?15.85%?genes,showing difference in expression,were obtained from different generations of progeny,70%of which had additive expression,and more than 18%showed expression bias?BT-F₁=414,BT-F₂=511,TB-F₁=455,TB-F₂=514?.Interestingly,some of the expression bias genes?139?could be inherited in different generations.More than 3%of the homologous genes were silenced and specifically expressed,and approximately 0.3%had a genomic imprinting phenomenon.The multiple expression patterns of homologous genes provide a foundation for researching the molecular mechanism of heterosis in allodiploid reciprocal hybrid lineages.Four expression bias genes,CFB,TYR,txndr1 and nectin2,were selected and determined by qRT-PCR.The results showed that the expression level of homologous gene CFB derived from BSB was over expressed than that derived from TC in one-month-old BT-F₁,as well as TYR in two-year-old BT-F₁,while the expression level of nectin2 from TC was significantly higher than that from BSB in the muscle and brain of two-year-old BT-F₂,as well as txndr1 in one-month-old TB-F₁.However,the expression level of gene txndr1 derived from BSB was significantly higher than that from TC in three-month-old TB-F₁.These results indicated that the expression bias of homologous genes could transform dynamically in different tissues and at different development stages of the hybrid progenies from BSB and TC.2.The research results showed that the gene expression of 18S rRNA in BT-F₅ was unstable.In the BT-F₅,some individual just expressed the 18S rRNA genes from TC,while others expressed the 18S rRNA genes from both BSB and TC,which means that nucleolar dominance was still not established in the fifth generation of such hybrid progeny.The establishment of nucleolar dominance maybe need five or more generations in the hybrid progeny of blunt snout bream and top mouth culter.In summary,the hybridization could transform dynamicly two or more genomes between different species,which is one of the broad breeding techniques.The variations of gene regulation mechanism,such as gene silencing,homoeologous genes expression bias,expression level dominance and genomic imprinting,provide insight into the molecular mechanism of heterosis.The phenomenon that nucleolar dominance in BT-F₅ had not yet been established completely,indicated that the eatablishment of nucleolar dominance in BT hybrid lineages requires more generations.