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| Fonte: protist.i.hosei.ac.jp - images - Collodictyon. |
Cientistas da Universidade de Oslo identificaram o que parece ser um microorganismo dos mais primitivos. Esse fóssil vivo foi encontrado a mais de 20 anos em um lago ao sul da capital da Noruega, mas somente agora a importância do achado foi notada. Segundo Kamran Shalchian-Tabrizi, um dos autores do artigo, "nenhum outro grupo de organismos descende de tão perto das raízes da árvore da vida". Este microorganismo "se desenvolveu há cerca de um bilhão de anos, com margem de erro de cem milhões de anos", afirmou.
Para ler mais: veja.abril.com.br - ciencia.
Resumo do artigo original:
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Collodictyon — An Ancient Lineage in the Tree of Eukaryotes.
Sen Zhao†,1, Fabien Burki†,2, Jon Bråte1, Patrick J. Keeling2, Dag Klaveness1 and Kamran Shalchian-Tabrizi*,1
+ Author Affiliations:
1Microbial Evolution Research Group, Department of Biology, University of Oslo, Oslo, Norway
2Canadian Institute for Advanced Research, Botany Department, University of British Columbia, Vancouver, British Columbia, Canada
*Corresponding author: E-mail: kamran@bio.uio.no.
Abstract
The current consensus for the eukaryote tree of life consists of several large assemblages (supergroups) that are hypothesized to describe the existing diversity. Phylogenomic analyses have shed light on the evolutionary relationships within and between supergroups as well as placed newly sequenced enigmatic species close to known lineages. Yet, a few eukaryote species remain of unknown origin and could represent key evolutionary forms for inferring ancient genomic and cellular characteristics of eukaryotes. Here, we investigate the evolutionary origin of the poorly studied protist Collodictyon (subphylum Diphyllatia) by sequencing a cDNA library as well as the 18S and 28S ribosomal DNA (rDNA) genes. Phylogenomic trees inferred from 124 genes placed Collodictyon close to the bifurcation of the “unikont” and “bikont” groups, either alone or as sister to the potentially contentious excavate Malawimonas. Phylogenies based on rDNA genes confirmed that Collodictyon is closely related to another genus, Diphylleia, and revealed a very low diversity in environmental DNA samples. The early and distinct origin of Collodictyon suggests that it constitutes a new lineage in the global eukaryote phylogeny. Collodictyon shares cellular characteristics with Excavata and Amoebozoa, such as ventral feeding groove supported by microtubular structures and the ability to form thin and broad pseudopods. These may therefore be ancient morphological features among eukaryotes. Overall, this shows that Collodictyon is a key lineage to understand early eukaryote evolution.
Key words:
- 18S and 28S rDNA
- Collodictyon
- Diphyllatia
- tree of life
- phylogenomics
- cDNA
- pyrosequencing
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