Modeling Interactions between Transposable Elements and the Plant Epigenetic Response: A Surprising Reliance on...

Area of Science:

• Genomics
• Epigenetics
• Molecular Biology

Background:

• Transposable elements (TEs) constitute the majority of plant DNA.
• Plants epigenetically silence TEs using small interfering RNAs (siRNAs) and DNA methylation.
• Two main silencing pathways exist: one involving 21-22 nt siRNAs and another, RNA-dependent DNA methylation (RdDM), using 24 nt siRNAs.

Purpose of the Study:

• To develop a systems-level deterministic model of TE propagation and host silencing responses.
• To investigate the necessity of two overlapping silencing pathways.
• To explore the relationship between host silencing efficiency and TE deletion rates.

Main Methods:

• Developed a deterministic model simulating active TE propagation, host responses, and TE silencing.
• Fitted the model to biological data to analyze pathway interactions and dependencies.
• Analyzed model predictions regarding the energetic costs and efficiency of silencing mechanisms.

Main Results:

• The model demonstrates that RNA-dependent DNA methylation (RdDM) effectively silences TEs, even with weak initial RNAi.
• Reinforcement by RdDM is essential for efficient counteraction of TE propagation.
• Low TE deletion rates correlate with fewer active TEs, suggesting retained methylated TEs enhance silencing efficiency.

Conclusions:

• A small amount of RNA interference initiates TE silencing, but RdDM is vital for robust silencing.
• The retention of methylated TEs, rather than deletion, may explain the large size of plant genomes.
• This study provides a systems-level understanding of TE-host interactions and epigenetic regulation in plants.