Multimegabase silencing in nucleolar dominance involves siRNA-directed DNA methylation and specific methylcytosine-binding proteins.
In genetic hybrids, the silencing of nucleolar rRNA genes inherited from one progenitor is the epigenetic phenomenon known as nucleolar dominance. An RNAi knockdown screen identified the Arabidopsis de novo cytosine methyltransferase, DRM2, and the methylcytosine binding domain proteins, MBD6 and MBD10, as activities required for nucleolar dominance. MBD10 localizes throughout the nucleus, but MBD6 preferentially associates with silenced rRNA genes and does so in a DRM2-dependent manner. DRM2 methylation is thought to be guided by siRNAs whose biogenesis requires RNA-DEPENDENT RNA POLYMERASE 2 (RDR2) and DICER-LIKE 3 (DCL3). Consistent with this hypothesis, knockdown of DCL3 or RDR2 disrupts nucleolar dominance. Collectively, these results indicate that in addition to directing the silencing of retrotransposons and noncoding repeats, siRNAs specify de novo cytosine methylation patterns that are recognized by MBD6 and MBD10 in the large-scale silencing of rRNA gene loci.
Preuss
Sasha B
SB
Biology Department, Washington University, St. Louis, MO 63130, USA.
Costa-Nunes
Pedro
P
Tucker
Sarah
S
Pontes
Olga
O
Lawrence
Richard J
RJ
Mosher
Rebecca
R
Kasschau
Kristin D
KD
Carrington
James C
JC
Baulcombe
David C
DC
Viegas
Wanda
W
Pikaard
Craig S
CS
D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D020029:Base Pairing / Q000235:genetics; D002466:Cell Nucleolus / Q000235:genetics*; D003596:Cytosine / Q000378:metabolism*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D019175:DNA Methylation; D021901:DNA, Intergenic; D020868:Gene Silencing; D006570:Heterochromatin / Q000378:metabolism; D008954:Models, Biological; D009697:Nucleolus Organizer Region / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D034622:RNA Interference; D018749:RNA, Plant / Q000378:metabolism; D012335:RNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism*
D029681:Arabidopsis Proteins; D021901:DNA, Intergenic; D006570:Heterochromatin; D018749:RNA, Plant; D012335:RNA, Ribosomal; D034741:RNA, Small Interfering; D003596:Cytosine; D004248:DNA (Cytosine-5-)-Methyltransferases