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Three
domains or two? Outlook upon evolution of Prokaryota and
the origin of Eukaryota
Abstract:
Evolutionary
relationships among prokaryotes and the origin of eukaryotes are discussed
in
this review. Molecular data of rRNA sequences derived from
different organisms led Woese and
collaborators to propose the three-domain universal tree of all
living organisms consisting of archaebacteria (Archaea), eubacteria
(Bacteria) and eukaryotes (Eukarya). Since its
introduction to the
science, the proposal has been widely accepted among biologists as
an evolutionary paradigm. However, this proposal, based primarily
on genes involved in the information transfer processes, is inconsistent
with the ultrastructural characteristics of prokaryotes, the
phylogenies of many genes and
highly conserved proteins, and it pro ides no explanation as to
the differences seen between different
groups of organisms. A second alternate proposal for the evolution
of major groups of prokaryotes
and the origin of eukaryotes has emerged from extensive
analyses of numerous con-served
indels found in various proteins. This proposal discerns only two
domains, Procaryotae and Eucaryotae. Among the
former group, two subdomains, Monodermata and Didermata,
are distinguished.
In view of the two-domain concept, all eukaryotic cells are
descendants of the ancestral chimera that arose by a unique
fusion event between an archaebacterium and a Gram-negative eubacterium.
The new proposal calls into ąuestion the validity of the three
domain model and the assignment
of domain status to Archaea, as well as the idea of
eukaryotes having been directly descended
from the archaebacterial ancestor.
l. Introduction.
2. Principles of current evolutionary paradigm. 3. Incongruities
within the evolutionary paradigm. 4. Critique of
validity of the three domain proposal. 5. An alternate
proposal for evolution of Prokaryota. 6. Position of
archaeabacteria in a new evolutionary model. 7. The origin
and phylogenetic relationships
among diderm bacteria. 8. Evolutionary relationship between Eukaryota
and proteobacteria,
9. Synthesis of the new proposal for evolution of Prokaryota
and the origin of Eukaryota |
