Loss of Small-RNA-Directed DNA Methylation in the Plant Cell Cycle Promotes Germline Reprogramming and Somaclonal...

Area of Science:

• Plant molecular biology
• Epigenetics
• Genomics

Background:

• 5-methylcytosine is crucial in plant genomes, existing in CG and non-CG contexts.
• CG methylation is guided by DNA replication, while non-CG methylation relies on histone modifications and small RNA guides.

Purpose of the Study:

• To investigate genome-wide cytosine methylation dynamics throughout the plant cell cycle.
• To understand how methylation patterns are maintained or altered during cell division and replication.

Main Methods:

• Utilized immortalized Arabidopsis cell suspensions.
• Sorted replicating nuclei to analyze cell cycle-specific methylation dynamics.
• Performed genome-wide methylome analysis.

Main Results:

• Symmetric CG and CHG methylation are retained in actively dividing cells; CHH methylation is depleted.
• mCG methylation becomes transiently asymmetric during S phase but is restored in G2.
• mCHG remains asymmetric throughout the cell cycle, and ectopic CHG methylation arises with associated siRNAs and H3K9me2.
• Spontaneous epialleles are maintained by siRNA and H3K9me2, independent of the canonical RNA-directed DNA methylation (RdDM) pathway.

Conclusions:

• Symmetric CG and CHG methylation are selectively maintained during plant cell division.
• Epigenetic variation in plants may arise from the loss of small-RNA-directed non-CG methylation during DNA replication, potentially facilitating germline reprogramming.