Genome-wide DNA Methylation Analysis of Mantle Edge and Mantle Central from Pearl Oyster Pinctada fucata martensii

DNA methylation is a type of epigenetic modification that alters gene expression without changing the DNA sequence and mediates some cases of phenotypic plasticity. In this study, we identified six DNA methyltransferase (DNMT) genes and two methyl-CpG binding domain protein2 (MBD2) gene from Pinctada fucata martensii. We also analyzed the genome-wide DNA methylation levels of mantle edge (ME) and mantle central (MC) from P. f. martensii via methylated immunoprecipitation sequencing (MeDIP-Seq). Results revealed that both ME and MC had 122 million reads, and had 58,702 and 55,721 peaks, respectively. The obtained methylation patterns of gene elements and repeats showed that the methylation of the protein-coding genes, particularly intron and coding exons (CDSs), was more frequent than that of other genomic elements in the pearl oyster genome. We combined the methylation data with the RNA-seq data of the ME and MC of P. f. martensii and found that promoter, CDS, and intron methylation levels were positively correlated with gene expression levels except the highest gene expression level. We also identified 313 differential methylation genes (DMGs) and annotated 212 of them. These DMGs were significantly enriched in 30 pathways, such as amino acid and protein metabolism, energy metabolism, terpenoid synthesis, and immune-related pathways. This study comprehensively analyzed the methylomes of biomineralization-related tissues and helped enhance our understanding of the regulatory mechanism underlying shell formation.