Discovery of DNA silencing mechanism reveals how plants protect their genome

Published in the April 28th issue of the journal PLoS Genetics, the finding contributes to advancing our understanding of a broad range of biological processes in both plants and animals, opening the door to applications in cancer therapy and agriculture.

In everything from protein synthesis to gene expression to development, living cells depend critically for their survival on the successful functioning of their DNA. Certain DNA elements such as transposons, fragments of DNA that replicate within an organism's genome, can however disrupt this functioning and disable genes. To defend against such harmful elements, eukaryotic cells form inactive tightly-packed DNA called heterochromatin, whose dense structure serves to repress (“silence”) the expression of nearby gene sequences and protect the genome.

Earlier research identified the enzyme HDA6 as playing a key role in such “hetrochromatin silencing” in the model plant Arabidopsis, but the mechanism involved remained unclear. In order to clarify this mechanism, the research group investigated the involvement of HDA6 in two processes: DNA methylation, an epigenetic modification that changes the structure of DNA without altering its sequence, and the modification of histone, the main component of chromatin.

Through a genome-wide comparison, the researchers were able to show that plants with repressed HDA6 function are not able to silence harmful DNA elements, suggesting that the enzyme plays an important role in gene silencing. Further investigation revealed that HDA6 binds directly to transposons and silences their activity through specific histone modifications, and that another enzyme, the DNA methyltransferase MET1, cooperates with HDA6 in this gene silencing.
Together, the findings establish for the first time that MET1-mediated DNA methylation and HDA6-mediated histone modification work together in repressing harmful DNA elements. By shedding light on the complex interplay between these two processes, the findings provide valuable insight on how plants and animals have evolved to protect their genome from harmful DNA, contributing to applications in areas such as cancer therapy and agriculture.

For more information, please contact:
Motoaki Seki
Plant Genomic Network Research Team
RIKEN Plant Science Center
Tel: +81-(0)45-503-9587 / Fax: +81-(0)45-503-9584
Ms. Tomoko Ikawa (PI officer)
Global Relations Office
RIKEN
Tel: +81-(0)48-462-1225 / Fax: +81-(0)48-463-3687
Email: koho@riken.jp

Reference:
To TK, Kim J-M, Matsui A, Kurihara Y, Morosawa T, et al. (2011) Arabidopsis HDA6 Regulates Locus-Directed Heterochromatin Silencing in Cooperation with MET1. PLoS Genet 7(4): e1002055. doi:10.1371/journal.pgen.1002055

About the RIKEN Plant Science Center
With rapid industrialization and a world population set to top 9 billion within the next 30 years, the need to increase our food production capacity is more urgent today than it ever has been before. Avoiding a global crisis demands rapid advances in plant science research to boost crop yields and ensure a reliable supply of food, energy and plant-based materials.

The RIKEN Plant Science Center (PSC), located at the RIKEN Yokohama Research Institute in Yokohama City, Japan, is at the forefront of research efforts to uncover mechanisms underlying plant metabolism, morphology and development, and apply these findings to improving plant production. With laboratories ranging in subject area from metabolomics, to functional genomics, to plant regulation and productivity, to plant evolution and adaptation, the PSC's broad scope grants it a unique position in the network of modern plant science research. In cooperation with universities, research institutes and industry, the PSC is working to ensure a stable supply of food, materials, and energy to support a growing world population and its pressing health and environmental needs.