Journal
PLANT MOLECULAR BIOLOGY
Volume 43, Issue 2-3, Pages 163-177Publisher
KLUWER ACADEMIC PUBL
DOI: 10.1023/A:1006471009225
Keywords
amphiplasty; chromatin; cytosine methylation; histone acetylation; nucleolus organizer; RNA polymerase I; rRNA genes; transcription
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Nucleolar dominance is a phenomenon in hybrids or allopolyploids in which nucleoli form on chromosomes inherited from only one of the two parents. The molecular basis for nucleolar dominance is the transcription by RNA polymerase I of only one parental set of ribosomal RNA genes (rRNA genes). These rRNA genes are clustered by the hundreds, or thousands, of copies, often spanning tens of millions of basepairs of chromosomal DNA at loci known as nucleolus organizer regions (NORs). Enforcement of nucleolar dominance appears to be accomplished by selectively silencing one set of rRNA genes via chemical modifications of chromatin. However, the mechanisms responsible for initially discriminating among the parental sets of rRNA genes and establishing nucleolar dominance remain unclear. Possibilities include mechanisms that act on each rRNA gene or mechanisms that affect whole NORs or even larger chromosomal domains. This review provides a historical perspective of nucleolar dominance research, explores the most popular hypotheses and their shortcomings, and offers some speculations concerning alternative hypotheses to be considered.
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