Multilayered epigenetic control of persistent and stage-specific imprinted genes in rice endosperm

In angiosperms, epigenetic profiles for genomic imprinting are established before fertilization. However, the causal relationships between epigenetic modifications and imprinted expression are not fully understood. In this study, we classified 'persistent' and 'stage-specific' imprinted genes on the basis of time-course transcriptome analysis in rice (Oryza sativa) endosperm and compared them to epigenetic modifications at a single time point. While the levels of epigenetic modifications are relatively low in stage-specific imprinted genes, they are considerably higher in persistent imprinted genes. Overall trends revealed that the maternal alleles of maternally expressed imprinted genes are activated by DNA demethylation, while the maternal alleles of paternally expressed imprinted genes with gene body methylation (gbM) are silenced by DNA demethylation and H3K27me3 deposition, and these regions are associated with an enriched motif related to Tc/Mar-Stowaway. Our findings provide insight into the stability of genomic imprinting and the potential variations associated with endosperm development, different cell types and parental genotypes. Time-course analysis of rice imprinted genes revealed persistent and stage-specific imprinted genes. These two classes showed differences in the degree of epigenetic status and biased expression in a temporal and spatial manner in the endosperm.