2-AIN-505, 2-AIN-251: Seminár z bioinformatiky (1) a (3)
Zima 2016
Abstrakt

Alexandros A. Pittis, Toni Gabaldon. Late acquisition of mitochondria by a host with chimaeric prokaryotic ancestry. Nature, 531(7592):101-104. 2016.

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Abstract:

The origin of eukaryotes stands as a major conundrum in biology. Current evidence
indicates that the last eukaryotic common ancestor already possessed many
eukaryotic hallmarks, including a complex subcellular organization. In addition, 
the lack of evolutionary intermediates challenges the elucidation of the relative
order of emergence of eukaryotic traits. Mitochondria are ubiquitous organelles
derived from an alphaproteobacterial endosymbiont. Different hypotheses disagree 
on whether mitochondria were acquired early or late during eukaryogenesis.
Similarly, the nature and complexity of the receiving host are debated, with
models ranging from a simple prokaryotic host to an already complex
proto-eukaryote. Most competing scenarios can be roughly grouped into either
mito-early, which consider the driving force of eukaryogenesis to be
mitochondrial endosymbiosis into a simple host, or mito-late, which postulate
that a significant complexity predated mitochondrial endosymbiosis. Here we
provide evidence for late mitochondrial endosymbiosis. We use phylogenomics to
directly test whether proto-mitochondrial proteins were acquired earlier or later
than other proteins of the last eukaryotic common ancestor. We find that last
eukaryotic common ancestor protein families of alphaproteobacterial ancestry and 
of mitochondrial localization show the shortest phylogenetic distances to their
closest prokaryotic relatives, compared with proteins of different prokaryotic
origin or cellular localization. Altogether, our results shed new light on a
long-standing question and provide compelling support for the late acquisition of
mitochondria into a host that already had a proteome of chimaeric phylogenetic
origin. We argue that mitochondrial endosymbiosis was one of the ultimate steps
in eukaryogenesis and that it provided the definitive selective advantage to
mitochondria-bearing eukaryotes over less complex forms.