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Origin and Early Diversification of the Viridiplantae: Exploring the Biodiversity of the Green Algae

Project Contact: Michael Melkonian, University of Cologne

The Viridiplantae in the course of their evolution changed life on this planet once and for ever; they were the only group of photosynthetic eukaryotes capable of establishing themselves on land and have thus shaped terrestrial life since then. Many fundamental questions surrounding the origin and early diversification of the Viridiplantae, however, remain unsolved:

(1) What was the nature and gene composition of the likely ancestor of the Viridiplantae?

(2) What was the original habitat of the earliest Viridiplantae (marine, freshwater, terrestrial)?

(3) Do any Viridiplantae exist that diverged before “the great divide”, i.e. before the split into Chlorophyta and Streptophyta?

(4) What is the fundamental difference between Chlorophyta and Streptophyta based on their transcriptomes?

(5) What was the impact of lateral gene transfer (from bacteria) on the early evolution of the Viridiplantae and the Chlorophyta/Streptophytra?

(6) Why has genome reduction accompanied the early diversification of the Chlorophyta and how many times have picoplanktonic organisms evolved within this lineage?

(7) What has triggered the evolution of the phycoplast and how did this affect the evolution of cell walls and multicellularity in the Chlorophyta?

(8) How many times were flagella lost in the green algae and what were the implications for mitosis, cytokinesis and sexual reproduction?

(9) What is the likely sister group to the embryophytes in the streptophyte algae?

(10) What were the changes in the transcriptome that accompanied the evolution of multicellularity, the phragmoplast, apical growth, gravitropism and plasmodesmata in the streptophyte green algae?

(11) How many times were terrestrial habitats colonized during the evolution of the Viridiplantae and how has the transcriptome responded in different lineages to various stress conditions involved (salinity, dryness, temperature, UV light) in this adaptation?

Based on these 11 fundamental questions concerning the origin and early diversification of the Viridiplantae, taxa were selected for sequencing considering the following criteria:

(i) The broadest representation of genetic diversity known in the green algae

(ii) All taxa readily available as clonal and/or axenic strains

(iii) Considerable knowledge about the biology of the organisms exists or is being obtained through ongoing studies

(iv) Consideration of ecological importance or biotechnological potential in selecting taxa.

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