Nucleotide substitutions in rDNA of evolutionarily static angiosperm groups

• Published in: Biology bulletin reviews Vol. 1; no. 2; pp. 110 - 124
• Main Authors: Chupov, V. S., Machs, E. M.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01-03-2011
• Subjects: Biochemistry; Biomedical and Life Sciences; Cell Biology; Ecology; Life Sciences; Zoology; rDNA; CpNpG sites; epigenetic evolution; DNA methylation; CpG; mutational pressure; direction of substitutions
• ISSN: 2079-0864; 2079-0872
• DOI: 10.1134/S2079086411020046

In this study we examine nucleotide substitutions in rDNA ITS1 of a number of evolutionarily static angiosperm taxa. It has been demonstrated that, in the majority of cases, cytosine-to-thymine substitutions in CpG dinucleotides prevail. The rate of cytosine-to-thymine substitutions in other neighboring positions is on the average twice as small. The rate of all other substitution types is 4–10 times less than the rate of cytosine-to-thymine substitutions in CpG dinucleotides. We hypothesize that, in evolutionarily static angiosperm taxa, the mutational “burn-out” of cytosine, especially intense in CpG sequences, and accumulation of TpG dinucleotides take place. The burn-out of cytosine is overcompensated in evolutionarily active sections of phylogenetic branches, where rDNA is saturated with cytosine and guanine. It is demonstrated that such a multidirectional mutational process in rDNA may be a model of context-dependent epigenetic changes in genomic regulatory elements during evolution.