A review in Annals of Botany recently introduced a potential link between rDNA homogenization and epigenetics.  Nicotiana are ideal for studying rDNA evolution because phylogenetic reconstruction of DNA sequences has revealed patterns of species divergence and their parents.  Previous studies showed that polyploids formed over widely different timeframes, enabling comparative and temporal studies of rDNA structure, activity and chromosomal distribution. 

The review propose that rDNA epigenetic expression patterns established even in F1 hybrids have a material influence on the likely patterns of divergence of rDNA.  It is the active rDNA units that are vulnerable to homogenization, which probably acts to reduce mutational load across the active array.  Those rDNA units that are epigenetic silenced may less vulnerable to sequence homogenization.

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