Massive RNA editing in ascetosporean mitochondria

Adenosine-to-inosine(A-to-I) substitution type of RNA editing is mediated
by adenosine deaminase acting on RNA (ADAR) and is involved in various
essential cellular functions. As ADAR functions in the metazoan nucleus,
it may have evolved from adenosine deaminase acting on tRNA in the
metazoan ancestor. Although ADAR has not been detected in fungi and
early-branching opisthokonts, it has not been explored in other eukaryotic
lineages. Here, we detected and analyzed ADAR from two novel rhizarian
amoebae and determined that other protists also possess ADAR. This finding
indicates that ADAR may have originated from the last common ancestor of
eukaryotes (LECA). Furthermore, the ADAR of the rhizarian amoeba is
localized in its mitochondria and may be involved in the massive RNA
editing in the mitochondria. Such complex RNA editing in the rhizarian
amoeba may have a function to mask some lethal mutations in the
mitochondrial genomes, which possibly contributes to the acceleration of
diversification instead of the increase of future extinction risk.