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Researchers sequenced 43 new transcriptomes from Zygnematophyceae algae and combined them with existing data to create a comprehensive evolutionary tree with 104 samples, revealing deep genetic divisions within this group that is the closest algal relative to land plants. The analysis uncovered ancient radiation events and showed that most multicellular Spirogyrales emerged after significant genetic divergence from their unicellular relatives. This phylogenomic framework provides crucial insights into the evolutionary history and genetic diversity needed to understand how plants initially adapted to colonize land.
Why it matters
Understanding the genetic makeup and evolutionary relationships of land plants' closest algal relatives helps scientists identify the key adaptations that enabled plants to transition from aquatic to terrestrial environments, one of the most important evolutionary events in Earth's history. This knowledge could inform agricultural improvements and help predict how plants might adapt to changing environments.
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by Maaike J. Bierenbroodspot, Cäcilia F. Kunz, Elisa S. Goldbecker, Maike Lorenz, Iker Irisarri, Thomas Pröschold, Tatyana Darienko, Jan de Vries
Discerning the nature of the last common ancestor of land plants (embryophytes) and algae allows to retrace the adaptations that ushered in the conquest of land by plants. For this, the closest streptophyte algal relatives of embryophytes hold key information. Albeit initially coming as a surprise due to their plain body plans, all major phylogenomic efforts have concluded that the Zygnematophyceae are the algal sisters to land plants. The Zygnematophyceae are the streptophyte algal class with the greatest species richness and while we now have ample genome information on a few select members of zygnematophytes, our understanding of the genomic divergence as well as genetic potential for key traits is limited by a lack of phylodiverse data that accounts for this diversity and integrates it into a phylogenomic framework. We here sequenced 43 new transcriptome datasets for the Zygnematophyceae and built a phylogenomic tree based on a total of 104 zygnematophyceaen transcriptomes and 2243 loci. We recover a deep genetic structure for the Zygnematophyceae: Despite the deep split between Spirogyrales and their unicellular sister group Desmidiales, most Spirogyrales emerged after pronounced genetic divergence, accommodating the attainment of multicellularity and divergent traits such as unique cell and plastid division. Overall, our data capture signatures of massive ancient radiations that could only be revealed thanks to a phylodiverse sampling. Recognizing the deep genetic divergences and a vast evolutionary history of the Zygnematophyceae are key to illuminate the nature of the algal progenitors of land plants.
Source: A deep genetic structure phylogenomically frames the closest algal relatives of land plants