Methanogenesis and its key small-molecule methyltransferase Mtr complex are poorly understood despite their pivotal role in Earth's global carbon cycle. Mtr complex is encoded by a conserved mtrEDCBAFGH operon in most methanogens. Here we report that two discrete lineages, Methanococcales and Methanomicrobiales, have a non-canonical mtr operon carrying two copies of mtrA resulted from an ancient duplication. Compared to MtrA-1, MtrA-2 acquires a distinct transmembrane domain through domain shuffling and gene fusion. However, the non-transmembrane domains (MtrA domain) of MtrA-1 and MtrA-2 are homogenized by gene conversion events lasting throughout the long history of these extant methanogens (over 2,410 million years). Furthermore, we identified a possible recruitment of ancient non-methanogenic methyltransferase genes to establish the methanogenesis pathway. These results not only provide novel evolutionary insight into the methanogenesis pathway and methyltransferase superfamily, but also suggest an unanticipated long-lasting effect of gene conversion on gene evolution in a convergent pattern.
- Received July 6, 2015.
- Accepted September 14, 2015.
- Copyright © 2015 Author et al.
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