Replication-uncoupled MET1/DNMT1 activity shapes inheritance of DNA methylation

Area of Science:

• Epigenetics and Genomics
• Molecular Biology
• Plant Science

Background:

• Cytosine methylation at CG sites (mCG) is crucial for gene regulation.
• Maintenance of mCG during DNA replication is proposed to be semiconservative.
• Mechanisms of mCG maintenance and their conservation across eukaryotes are not fully understood.

Purpose of the Study:

• To investigate the dynamics of mCG maintenance beyond DNA replication.
• To explore the role of the major CG methyltransferase 1 (MET1) in plants.
• To compare mCG maintenance mechanisms between plants and mammals.

Main Methods:

• Development of live-cell sensors to track mCG dynamics.
• Genetic dissection of MET1 function in Arabidopsis.
• Single-molecule duplex sequencing to analyze methylation patterns.

Main Results:

• mCG maintenance extends beyond DNA replication in Arabidopsis, with MET1 associated with chromatin from S to G2 phase.
• MET1, like mammalian DNMT1, methylates nucleosome-associated DNA.
• Methylation is constrained by nucleosomal DNA accessibility and only partly templated by hemimethylated sites.

Conclusions:

• MET1/DNMT1 exhibit nucleosome-constrained de novo activity, influencing mCG recovery and variation.
• mCG maintenance mechanisms show conservation between plants and mammals.
• This study reveals a broader role for methyltransferases in epigenetic regulation beyond replication-coupled maintenance.