Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 116, Issue 19, Pages 9652-9657Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1821435116
Keywords
DNA methylation; DNA demethylation; epigenetics; rice; pollen
Categories
Funding
- NIFA-USDA [2013-67012-21112]
- NSF [IOS-1025890]
- NIH [S10 OD018174, R01-GM069415]
- Japan Society for the Promotion of Science (JSPS) [JP15K07262]
- Ministry of Education, Culture, Sports, Technology and Science (MEXT) [JP16H06471]
- MEXT [17H058452]
- JSPS [16K14742]
- BBSRC [BBS/E/J/000PR9773] Funding Source: UKRI
- Grants-in-Aid for Scientific Research [16K14742] Funding Source: KAKEN
- NIFA [2013-67012-21112, 577566] Funding Source: Federal RePORTER
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Epigenetic reprogramming is required for proper regulation of gene expression in eukaryotic organisms. In Arabidopsis, active DNA demethylation is crucial for seed viability, pollen function, and successful reproduction. The DEMETER (DME) DNA glycosylase initiates localized DNA demethylation in vegetative and central cells, so-called companion cells that are adjacent to sperm and egg gametes, respectively. In rice, the central cell genome displays local DNA hypomethylation, suggesting that active DNA demethylation also occurs in rice; however, the enzyme responsible for this process is unknown. One candidate is the rice REPRESSOR OF SILENCING 1a (ROS1a) gene, which is related to DME and is essential for rice seed viability and pollen function. Here, we report genome-wide analyses of DNA methylation in wild-type and ros1a mutant sperm and vegetative cells. We find that the rice vegetative cell genome is locally hypomethylated compared with sperm by a process that requires ROS1a activity. We show that many ROS1a target sequences in the vegetative cell are hypomethylated in the rice central cell, suggesting that ROS1a also demethylates the central cell genome. Similar to Arabidopsis, we show that sperm non-CG methylation is indirectly promoted by DNA demethylation in the vegetative cell. These results reveal that DNA glycosylase-mediated DNA demethylation processes are conserved in Arabidopsis and rice, plant species that diverged 150 million years ago. Finally, although global non-CG methylation levels of sperm and egg differ, the maternal and paternal embryo genomes show similar non-CG methylation levels, suggesting that rice gamete genomes undergo dynamic DNA methylation reprogramming after cell fusion.
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