| The Pacific oyster(Crassostrea gigas),is mainly distributed in the eastern coastal area of China.The oyster has been introduced from Japan since 80s in the twentieth Century.It has become an important marine breeding species in China due to its fast growing speed,adaptability and high yield.It has also become a research hotspot of relevant researchers.The main findings of this study are as follows:1.Comparation of genetic diversity and growth of C.gigas)between different inbreeding selection and self-fertilization selectionTo get stable and inheritable traits quickly,inbreeding is often used to obtain a pure line.However,this practice may cause a decline in the genetic diversity in the population.In this study we selected eight high-polymorphic microsatellite loci of C.gigas to investigate the genetic diversity,genetic structure,and growth of the fourth breeding generation(F4),the fifth breeding generation(F5)and the first selfing generation(selfing1).The growth data were analyzed at three temporal points.The experimental results showed that the eight microsatellite markers presented high polymorphism in the wild control group.All the indicators decreased significantly in the three inbreeding lines,and the average allele number(N_a)descended from 12.25 to 2.00,the average observed heterozygosity declined(H_o)from 0.538 to 0.449,and the average polymorphism information content(PIC)of the eight microsatellite markers decreased from 0.826 to 0.297.The eight loci deviated from the Hardy-Weinberg equilibrium in three inbreeding lines and the wild control group.Analysis of growth traits showed that,the growth index of the three inbreeding increased significantly compared to wild control.On the other hand,there were no significant differences in shell length and shell width at the three temporal points(except for shell width at 330 days and shell length at 630 days).However,the traits of shell height and wet weight of F5 generation were significantly higher than those of F4 generation.Moreover,there was no significant difference between selfing 1 generation and F4 generation.Overall,the F5 generation inbreeding lines could be used continuously for growth traits(such as shell height and wet weight)selection,although the diversity may decline as a trade-off due to brother-sister self-fertilization.2.Analysis of whole genome methylation on glycogen conent trait of C.gigas base on MethyRAD technologyWith the success of the oyster genome assemblied,studies on oysters’genes,functions and phenotypes will come to a new stage.The content of glycogen is a very important trait,which could not only affect the qualiy and flavor of oysters,but also affect the resistance and survival rate of oyster.Therefore,in the second chapter,the regulation mechanism related to the content of oyster glycogen is preliminarily discussed from the point of epigenetic methylation.The results showed that:(1)The methylation of CpG was the main form of oyster’s methylation.Methylation sites mainly occur in exon and intron.,followed by upstream and intergenic.And 3’and5’non translational methylation levels were the lowest.The methylation sites of the same families cultured in different areas were almost in agreement with each other.To some extent,the result showed that methylation could be inherited.(2)The genes involved in the methylation sites of the four families were mainly focused on the basic activities of the oyster’s immunity,energy metabolism and signal transduction.It was presumed that the environment might affect the physiological characteristics of the individual by affecting the basic activity of oysters.Among them,glutathione-S-transferase,serine/threonine protein kinase and NADH dehydrogenase were related to the synthesis of glycogen.(3)GO enrichment analysis showed that the family differential methylation genes were significantly enriched in GO term,which was directly related to glycogen metabolism.These items included glycogen phosphorylase,glycogen synthase and glycogen debranched enzyme,which were directly related to glycogen synthesis,including genes such as serine/threonine protein kinase,phosphorylase b kinase and other genes involved in glycogen metabolism.There was a significant difference in the difference of methylation genes.The top 30 of GO term was related to fatty acids,amino acids and glucose metabolism(4)Among the KEGG metabolic pathways enriched by differentially methylated genes,most of the top 20were pathways related to fatty acids,amino acids,glucose metabolism and cell division,and signal transduction.This study infers that the methylation level of oyster genome plays an important role in regulation before transcription.On the one hand,it influences the expression of glycogen directly and indirectly related to glycogen to directly regulate glycogen content.On the other hand,it affects the glycogen through the metabolism of acids and fatty.The metabolic levels of fatty acids affect the metabolism of glucose respoundly.And energy metabolism can interact with the three major metabolisms,thereby indirectly regulating the glycogen content of oysters.Since the KTD and RS area locate on the north and south sides of the Shandong peninsula have different aquaculture environments such as sea water temperature,salinity,and the richness of food,it is speculated that environmental factors can affect the methylation level of oysters to a certain extent.But the regulation of the gloycegen content mechanism needs further study. |
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