Small RNAs guide histone methylation in Arabidopsis embryos

Area of Science:

• Plant Molecular Biology
• Epigenetics
• Developmental Biology

Background:

• Epigenetic reprogramming is crucial for gametogenesis and embryogenesis, resetting the genome for development.
• In flowering plants, heterochromatic marks persist in sperm, but asymmetric DNA methylation is largely lost.
• The re-establishment of gene silencing in the embryo, dependent on small RNAs, is not fully understood.

Purpose of the Study:

• To investigate the role of small RNAs in directing epigenetic modifications during *Arabidopsis thaliana* embryonic development.
• To elucidate the mechanism of de novo gene silencing in the early embryo.
• To determine the involvement of SUVH9 in establishing heterochromatin during embryogenesis.

Main Methods:

• Analysis of small RNA pathways and their role in epigenetic reprogramming.
• Histone modification assays, specifically focusing on histone H3 lysine 9 dimethylation (H3K9me2).
• DNA methylation analysis in *Arabidopsis thaliana* embryos.

Main Results:

• Small RNAs direct histone H3 lysine 9 dimethylation during *Arabidopsis thaliana* embryonic development.
• Asymmetric DNA methylation is re-established in conjunction with H3K9me2, guided by small RNAs.
• The de novo silencing mechanism is dependent on the catalytic domain of SUVH9, a Su(Var)3-9 homolog.

Conclusions:

• Small RNAs play a critical role in establishing heterochromatin through histone methylation during *Arabidopsis* embryogenesis.
• SUVH9 possesses catalytic activity essential for de novo gene silencing via H3K9me2 and DNA methylation.
• This study reveals a novel small RNA-directed silencing pathway crucial for embryonic development in plants.