Abstract
Genomic imprinting is an epigenetic phenomenon by which certain genes display monoallelic expression in a parent-of-origin-dependent manner. Hundreds of imprinted genes have been identified from several plant species. Here we identified, with a high level of confidence, 208 imprinted candidates from rice. Imprinted genes of rice showed limited association to the transposable elements, which is contrast to the findings in Arabidopsis. Generally, imprinting of rice is conserved within species, but intraspecific variations were confirmed here. Imprinting between cultivated rice and wild rice are likely similar. The imprinted genes of rice do not show significant selective signatures overall, which suggests that domestication imposes limited evolutionary effects on genomic imprinting of rice. Though the conservation of imprinting in plants is limited, here we prove that some loci tend to be imprinted in different species. In addition, our results suggest that differential epigenetic regulation between parental alleles can be established either prior to or post-fertilization. The imprinted 24-nt small RNAs, but not the 21-nt ones, likely involve the regulation of imprinting in an opposite parental-allele targeting manner. Together, our findings suggest that regulation of imprinting can be very diverse, and genomic imprinting as well as imprinted genes have essential evolutionary and biological significance.
