1 Probing early eukaryotic evolution using phylogenetic methods The Universal SSU rRNA Tree Wheelis et al. 1992 PNAS 89: 2930 Archezoa The SSU Ribosomal RNA Tree for Eukaryotes Mitochondria? Prokaryotic outgroup Animals Fungi Ciliates + Apicomplexa Stramenopiles Euglenozoa Giardia Trichomonas Plants / green algae Red algae Entamoebae Choanozoa Dictyostelium Physarum Microsporidia Percolozoa The Archezoa Hypothesis - primitively amitochondriate eukaryotes (Tom Cavalier-Smith 1983) Trichomonas Microsporidia Giardia ‘Tree’ courtesy of W. Ford Doolittle Entamoeba The Archezoa Hypothesis T. Cavalier-Smith (1983) • The Archezoa hypothesis would fall if: – Find mitochondrial genes on archezoan genomes – Find that archezoans branch among aerobic species with mitochondria – Find mitochondrion-derived organelles in archezoans
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The Universal SSU rRNA Tree Probing early eukaryotic Wheelis et al
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Probing early eukaryoticevolution using phylogenetic
methods
The Universal SSU rRNA TreeWheelis et al. 1992 PNAS 89: 2930
Archezoa
The SSU Ribosomal RNA Tree for Eukaryotes
Mitochondria?
Prokaryoticoutgroup
AnimalsFungi
Ciliates + ApicomplexaStramenopiles
Euglenozoa
GiardiaTrichomonas
Plants / green algae
Red algae
Entamoebae
Choanozoa
Dictyostelium
Physarum
Microsporidia
Percolozoa
The Archezoa Hypothesis - primitivelyamitochondriate eukaryotes
(Tom Cavalier-Smith 1983)
Trichomonas Microsporidia
Giardia‘Tree’ courtesy of W. Ford Doolittle Entamoeba
The Archezoa HypothesisT. Cavalier-Smith (1983)
• The Archezoa hypothesis would fall if:
– Find mitochondrial genes on archezoangenomes
– Find that archezoans branch amongaerobic species with mitochondria
• Evidence for Giardia and Trichomonas branching deeperthan other eukaryotes is based on trees made usingunrealistic assumptions (often PROTML)
• There is plenty of room for new hypotheses
If former archezoa containgenes from the mitochondrial
endosymbiont what happened tothe organelle?
Microsporidia are obligateintracellular parasites
Life cycle of microsporidia
Tree of Mitochondrial Hsp70
mtHsp70 has diverse roles in mitochondriaPfanner and Geissler 2001 Nature Reviews 2: 339-344
mtHsp70 also plays a role in assembly of Fe-S clusters - an essential function for yeast mitochondria (Lill & Kispal, 2000)
mtHsp70
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Microsporidial HSP70 have no obviousN-terminal targeting signal
Localisation of a mtHsp70 in Trachipleistophora
Western blot using an antibody to Th-mtHsp70
Infe
cted
cells
Spor
es
Rabb
it
Confocalmicroscopyusing anantibody toTh-mtHsp70
The Hsp70 protein islocalised to membranebound or electron densestructures.
Traditional fixationmethods show a doublemembrane
Microsporidian
Williams et al. 2002 Nature 418: 865-869
Host cell mitochondrion
Microsporidian‘mitochondrial remnant’
Trees are a good way of exploring thehistory of genes but care is needed!
• Making trees is not easy:– Among-site rate heterogeneity, “fastclock” species, shared nucleotide or aminoacid composition biases
– Different data sets may be affected byindividual phenomena to different degrees
– Biases need not be large if phylogeneticsignal is weak
• Phylogenetic analysis is frequently treated as ablack box into which data are fed (often gatheredat considerable cost) and out of which “The Tree”springs
• (Hillis, Moritz & Mable 1996, Molecular Systematics)