Endosymbiosis and endosymbiotic gene transfer

Plastids and mitochondria were once free-living prokaryotes – at the time of endosymbiosis they possessed all genes necessary for that free-living lifestyle. But today, organelle genomes are very highly reduced relative to the genomes of their free-living cousins. Chloroplast genomes encode about 5–10% as many proteins as free-living cyanobacteria, mitochondrial genomes encode about 1–3% as many proteins as free-living alpha-proteobacteria. But both organelles contain roughly as many proteins as their free-living prokaryotic relatives. To explain this, there is something called endosymbiotic gene transfer: During evolution, organelles relinquished many genes to the chromosomes of their host, but they also learned to reimport the nuclear-encoded products of transferred genes. Endosymbiotic gene transfer is much, much more widespread than is generally assumed. The thrust of our eariler work on this topic involved comparisons of selected genes from specific biochemical pathways. Currently, we are using genome-wide phylogenies of genes in sequenced genomes to obtain some quantitative estimates for the fraction of genes that eukaryotes acquired from organelles - both during primary and secondary endosymbioses. Of course, we are also interested not only in the "how much", but also in the "how" and "why" of endosymbiotic gene transfer, not to mention the more pressing question of why organelles have retained genomes at all.

Some papers on this topic are:

  • Martin W, Stoebe B, Goremykin V, Hansmann S, Hasegawa M, Kowallik KV (1998) Gene transfer to the nucleus and the evolution of chloroplasts. Nature 393:162–165.
  • Rujan T, Martin W (2001) How many genes in Arabidopsis come from cyanobacteria? An estimate from 386 protein phylogenies. Trends in Genetics 17:113–120.
  • Race HL, Herrmann RG, Martin W (1999) Why have organelles retained genomes? Trends in Genetics 15:364–370.
  • Henze K, Martin W (2001) How are mitochondrial genes transferred to the nucleus? Trends in Genetics 17:383–387.
  • Martin W (1999) Mosaic bacterial chromosomes – A challenge en route to a tree of genomes. BioEssays 21:99–104.
  • Martin W, Herrmann RG (1998) Gene transfer from organelles to the nucleus: How much, what happens and why? Plant Physiol. 118:9–17
  • Deane JA, Fraunholz M, SuV, Maier U-G, Martin W, Durnford DG, McFadden GI (2000): Evidence for nucleomorph to host nucleus gene transfer: light-harvesting complex proteins from cryptomonads and chlorarachniophytes. Protist 151:239–252.
  • Henze K, Schnarrenberger C, Martin W (2001) Endosymbiotic gene transfer: A special case of horizontal gene transfer germane to endosymbiosis, the origins of organelles and the origins of eukaryotes. In Horizontal Gene Transfer. Syvanen M, Kado C (eds). Academic Press, London. pp. 343–352.
  • Martin W (1996) Is something wrong with the tree of life? BioEssays 18:523–527.
  • Henze K, Badr A, Wettern M, Cerff R and Martin W (1995) A nuclear gene of eubacterial origin in Euglena gracilis reflects cryptic endosymbioses during protist evolution. Proc. Natl. Acad. Sci. USA 92:9122–9126.
  • Martin W, Brinkmann H, Savona C, Cerff R (1993) Evidence for a chimaeric nature of nuclear genomes: Eubacterial origin of eukaryotic glyceraldehyde-3-phosphate dehydrogenase genes. Proc. Natl. Acad. Sci. USA 90:8692–8696.


Prof. Dr. William F. Martin

Molekulare Evolution
Universitätsstraße 1
Gebäude: 26.13
Etage/Raum: 01.34
Tel.: +49 211 81-13011
Fax: +49 211 81-13554
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