Phylogenomic insights into the first multicellular streptophyte.

Area of Science:

• Evolutionary Biology
• Phylogenomics
• Algal Biology

Background:

• Streptophytes include land plants (embryophytes) and related algae, with Klebsormidiophyceae being crucial for understanding early land plant evolution.
• Klebsormidiophyceae inhabit diverse environments and possess traits relevant to terrestrialization, but their evolutionary history is unclear due to a lack of robust phylogenetic data.
• Understanding Klebsormidiophyceae evolution offers insights into the emergence of key traits in land plants.

Purpose of the Study:

• To establish a robust phylogenomic framework for the Klebsormidiophyceae.
• To reconstruct the evolutionary history of Klebsormidiophyceae, including habitat transitions and body plan evolution.
• To investigate the timing of key evolutionary events, such as multicellularity and land colonization within streptophytes.

Main Methods:

• Conducted a phylogenomic analysis using 24 new and 14 existing transcriptomic and genomic datasets.
• Employed advanced models to counteract systematic biases in phylogenetic reconstruction.
• Analyzed 845 loci using sophisticated mixture models to establish evolutionary relationships.

Main Results:

• Established a novel phylogenetic framework for Klebsormidiophyceae, dividing them into three orders and revealing a deep divergence over 830 million years ago.
• Reconstructed ancestral states indicating multiple transitions between aquatic and terrestrial habitats, with early land colonization by stem Klebsormidiales preceding embryophytes.
• Indicated that the last common ancestor of Klebsormidiophyceae was multicellular and likely filamentous, with unicellular forms being derived.

Conclusions:

• The study provides strong evidence for the early multicellularity of streptophytes, likely originating around a billion years ago.
• Klebsormidiophyceae played a significant role in the early colonization of land, with evolutionary trajectories distinct from embryophytes.
• The novel phylogenetic framework resolves long-standing questions about Klebsormidiophyceae evolution and provides a foundation for future research.