HORIZONTAL TRANSFER IN EUKARYOTES KIMBERLEY MC GRAIL FERNÁNDEZ GENOMICS

HORIZONTAL TRANSFER IN EUKARYOTES KIMBERLEY MC GRAIL FERNÁNDEZ GENOMICS

OVERVIEW INTRODUCTION MECHANISMS OF HGT IDENTIFICATION TECHNIQUES EXAMPLES - Wolbachia pipientis - Fungus - Plants - Drosophila ananassae - You are what you eat RELEVANCE AND CONTROVERSY CONCLUSIONS REFERENCES

INTRODUCTION Biological evolution proceeds from ancestry to descendants with modifications (Darwin) à Non-anastomosing phylogenetic trees Horizontal Gene Transfer (HGT) refers to the transfer of genes between organisms. It leads to evolutionary reticulations à Anastomosing phylogenetic trees Acquisition of foreign genes (evolutionary potential) Prokaryotes Eukaryotes Unicellular Multicellular

Wijayawardena et al. (2013)

MECHANISMS Donor and recipient must have a close relationship Phagocytosis/symbiosis (Mitochondria and plastids) Parasitism Mobile genetic elements Plasmids Viruses Transposable elements (TEs) The foreign genetic material has to successfully integrate into the germline Evasion of immune system, nucleases and proteases Genomic compatibility Population genetic processes: mutation, natural selection, genetic flow and genetic drift

Wijayawardena et al. (2013)

DETECTION TECHNIQUES Phylogenetic methods: Incongruence Phylogenetic-independent methods Codon-based approaches BLAST Wijayawardena et al. (2013) PCR- based approaches Fluorescent in situ hybridization (FISH), Southern, comparisons of protein structures, Chromosome/genome walking Comparative genome studies Biogeographical and ecological data COMBINATION!

PROKARYOTE! EUKARYOTE The presence of endosymbionts Wolbachia pipientis, within some eukaryotic germlines may facilitate bacterial gene transfers to eukaryotic host genomes. Transfers into the genomes of four insect and four nematode. Verified by molecular techniques as FISH in a Drosophila chromosome using a probe for a Wolbachia gene. Hotopp et al. (2007)

EUKARYOTE! EUKARYOTE Stagonospora nodorum ToxA Pyrenophora tritici-repentis The gene has not been found in closely related species. The mechanism of transfer could be related with the fusion of hyphae, the nucleuses were very close and the transfer took place. Sanders et al. (2006)

EUKARYOTE! EUKARYOTE Plant mitochondria genomes experience frequent horizontal transfer of genes. Mitochondria à Mitochondria Active DNA uptake system but no such system is known in plastids (propensity to fuse). Pseudogenes vs. functional genes Amborella trichopoda: massive HGT (20 of the 30 mitochondrial genes) à special opportunities for studying the evolutionary dynamics of HGT at the populations level. Richardson et al. (2006)

EUKARYOTE! EUKARYOTE Many TEs have been horizontally transferred among Drosophila species. Hundred-one events of HT have been proposed in Drosophila for 21 different elements: 5% non-ltr 42,6% LTR 52,4% DNA transposons The mechanism of HT vary from very simple ones, such a direct transfer (LTR), to more complex systems involving intermediate vectors. TEs-rich regions are specially prone to HGT, what suggests a functional role for TEs. Loreto et al. (2008)

Loreto et al. (2008)

YOU ARE WHAT YOU EAT, WHAT YOU LIVE ON, WHAT LIVES ON YOU, AND WHAT LIVES IN YOU Keeling et al. (2008)

RELEVANCE AND CONTROVERSY RELEVANCE: History of eukaryotic evolution (information) It may provide genes of novel function to the recipient genome The whole acquisition of intact genes and/or regulatory regions may allow species to evolve genes. Important contributor to genomic diversity. CONTROVERSY: Role of HGT? Vectors, donors and recipients? Unknown mechanisms Insufficient methodologies

CONCLUSIONS 1. HGT forms anastomosing phylogenetic trees. 2. The HGT has evolutionary potential because it allows the acquisition of foreign genes (generation of new biological diversity). 3. HGT is more frequent in prokaryotes but it also occurs in eukaryotes, where plays a more important role than it was though. 4. Transferred gene evolves according to the population genetic factors. 5. Detection techniques must be combined in order to detect the presence of HGT with no mistake. 6. The range of eukaryotic organisms subjected to HGT is really high. 7. Several behaviours and life-styles can enhance HGT.

REFERENCES Hotopp JC et al. 2007. Widespread lateral gene transfer from intracellular bacteria to multicellular eukaryotes. Science. 317(5845): 1753-6. Keeling PJ, Palmer JD. 2008. Horizontal transfer in eukaryotic evolution. Nat Rev Genet. 9(8):605-18. Review. Loreto EL, Carareto CM, Capy P. 2008. Revisiting horizontal transfer of transposable elements in Drosophila. Heredity. 100(6):545-54. Richardson AO, Palmer JD. 2007. Horizontal transfer in plants. J Exp Bot. 58(1):1-9. Sanders IR. 2006. Rapid disease emergence through horizontal gene transfer between eukaryotes. Trends Ecology Evolut. 21:656-658 Wijayawardena BK, Minchella DJ, DeWoody JA. 2013. Hosts, parasites, and horizontal gene transfer. Trends Parasitol.29(7):329-38.

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