IC4R005-Epigenomic-2016-20487381

Project Title

• Genome-wide mapping of cytosine methylation revealed dynamic DNA methylation patterns associated with genes and centromeres in rice

The Background of This Project

• DNA methylation is an epigenetic mark that can often lead to the repression of gene expression (1, 2). It is enriched in heterochromatin and, when present at regulatory sites, usually acts as a repressor of expression, most notably in transposons (3). However, it is also found over coding regions, where it likely does not directly affect transcription and is associated with moderately expressed genes (2, 4–6). In plants, DNA methylation occurs in three different contexts: CG, CHG, and CHH (where H is any nucleotide but G). In Arabidopsis, each context is maintained by different enzymes: MET1 for CG sites, CMT3 for CHG sites and DRM2 for CHH sites. CG and CHG sites are symmetric across the two DNA strands, which is thought to be important for the maintenance of methylation at these sites following DNA repli- cation. In contrast, CHH sites are not symmetric, and their methylation is mediated by RNA-directed DNA methylation pathways (RdDM), which use siRNAs to initiate de novo methylation (3). Cellular methylation states tend to persist during cell division, and recent studies in Arabidopsis have also shown that DNA methylation is faithfully inherited across generations (7, 8). Nonetheless, we are only beginning to understand how different methylation patterns from inbred parents may “interact” during the generation of their hybrid progeny (9, 10).
• In this project, the researchers generated integrative maps of whole-genome cytosine methylation profiles [bisulfite sequencing (BS-seq)] and transcriptional profiles (RNA-seq), to characterize two rice subspecies, Oryza sativa spp japonica [Nipponbare (NPB)] and Oryza sativa spp indica (93–11) and their two reciprocal hybrid off- spring. Using a combination of BS-seq, RNA-seq, and siRNA-seq, we were able to generate allele-specific patterns of methylation and transcription in the hybrids, and thus directly measure the degree to which these are altered between the corresponding parental and F1 chromosomes.

Labs working on this Project

• Department of Horticulture, University of Wisconsin-Madison, Madison, WI 53706, USA, and
• U.S. Department of Energy Joint Genome Institute, Walnut Creek, CA 94598, USA

Corresponding Author

• Jiming Jiang (jjiang1@wisc.edu)