RNA editing in metazoan mitochondria: staying fit without sex

Abstract

RNA editing subsumes a number of functionally different mechanisms which have in common that they change the nucleotide sequence of RNA transcripts such that they become different from what would conventionally be predicted from their gene sequences. RNA editing has now been found in the organelles of numerous organisms as well as in a few nuclear transcripts. Most recently, it was shown to affect tRNAs in the mitochondria of several animals. The occurrence and evolutionary persistence of RNA editing is perplexing since backmutations in the genes might be assumed rapidly to eliminate the need for 'correction' of the gene sequences at the posttranscriptional level. Here, we review the recent RNA editing systems discovered in animal mitochondria and propose that they have arisen as a mechanism counteracting the accumulation of mutations that occurs in asexual genetic system.

Extensive Loss of RNA Editing Sites in Rapidly Evolving Silene Mitochondrial Genomes: Selectionvs. Retroprocessing as the Driving Force

“…These findings provide insight into the forces that guide the evolution of RNA editing. For example, as noted previously , the negative relationship between mutation rate and the frequency of editing runs directly counter to predictions arising from the hypothesis that editing acts as a mutational buffer (Borner et al 1997;Horton and Landweber 2002). In addition, these findings raise central questions about the relative importance of adaptive and nonadaptive processes in the evolution of RNA editing, which we discuss below.…”

“…Various adaptive effects of RNA editing have been proposed, including a role in gene regulation (Hirose et al 1999;Farajollahi and Maas 2010), maintenance of alternative functional protein isoforms (Gott 2003;Farajollahi and Maas 2010), generation of genetic variation (Tillich et al 2006;Gommans et al 2009), optimization of genomic GC content (Jobson and Qiu 2008), nuclear control of selfish organelle genes (Burt and Trivers 2006), and mutational buffering (Borner et al 1997). In humans, there is evidence for divergent functional roles for products of the edited and unedited forms of apolipoprotein B (Powell et al 1987), but there is little evidence for the aforementioned adaptive mechanisms in plant organelles.…”

Evolution of the Mitochondrial DNA Control Region and Cytochrome b Genes and the Inference of Phylogenetic Relationships in the Avian Genus Lophura (Galliformes)

“…We suggest that RNA editing (Börner et al, 1997;Smith et al, 1997), which can generate a functional stop codon by cleavage after the downstream T (Fig. 2b, region B) and polyadenylation of the resulting transcript to form a UAA stop codon, is the most likely explanation for the observed CTG and TTG codons (see Discussion).…”

Intricacies and surprises of nuclear–mitochondrial co-evolution

“…The asexual evolution of mt genomes, which means absence of recombination and genome segregation typical of meiotic processes, is thought to have resulted in a gradual loss of fitness, which the eukaryotic cell has compensated for in order to maintain the function of this indispensable organelle [13]. In turn, mt evolution has probably been fuelled by access to the copious coding and recombination capacities of nuclear genomes and their effective mechanisms of protein evolution.…”

“…To fix the problem, the nucleus has provided an A9-N 1 -methyltransferase that stabilizes the cloverleaf [14]. Another example comes from marsupials, a group of non-placental mammals: here, mt-tRNA Asp is corrected by a C-to-U editing event [13]. Nuclear-mitochondrial coevolution has in some cases been pushed even further: in several protozoa, not a single tRNA is encoded in the mt genome and all mt tRNAs are imported from the nucleus [15].…”