Maize decrease in DNA methylation 1 targets RNA-directed DNA methylation on active chromatin.

Area of Science:

• Plant molecular biology
• Epigenetics
• Genomics

Background:

• DNA methylation is essential for controlling transposable elements and gene expression in plants.
• The chromatin remodeler Decrease in DNA methylation 1 (DDM1) is vital for DNA methylation maintenance and RNA-directed DNA methylation (RdDM) in maize (Zea mays).
• The precise role of DDM1 in the RdDM pathway remains incompletely understood.

Purpose of the Study:

• To investigate the genome-wide binding patterns of ZmDDM1 in maize.
• To elucidate the molecular mechanisms underlying DDM1's involvement in the RdDM pathway.
• To understand how ZmDDM1 contributes to epigenetic regulation in maize.

Main Methods:

• Chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) was employed to map ZmDDM1 occupancy across the maize genome.
• Bioinformatic analysis was used to identify DNA sequence motifs recognized by ZmDDM1.
• Co-immunoprecipitation assays were performed to assess interactions between ZmDDM1 and other RdDM components, such as ZmAGO4.

Main Results:

• ZmDDM1 binds to a specific 8-bp GC-rich DNA motif predominantly found in transcription start sites and euchromatic regions.
• 24-nucleotide small interfering RNAs (siRNAs) and CHH methylation were detected at the boundaries of ZmDDM1-occupied regions.
• ZmDDM1 physically interacts with ZmAGO4, a key protein in the RdDM pathway, and their binding sites largely overlap.
• ZmDDM1 occupancy is strongly correlated with ZmAGO4 binding sites, indicating a functional association.

Conclusions:

• ZmDDM1 is recruited to specific GC-rich motifs in euchromatic regions of the maize genome.
• Through chromatin remodeling, ZmDDM1 facilitates access for RdDM machinery, including ZmAGO4.
• These findings propose a model where ZmDDM1 acts as a crucial component of the RdDM pathway in maize, integrating DNA sequence recognition with chromatin modification for epigenetic control.