Phylogenomics reveals deep genetic structure in algal relatives of land plants

A phylogenomic study analyzing 104 zygnematophycean transcriptomes across 2,243 loci has recovered a deep genetic structure for the Zygnematophyceae, the streptophyte algal sister group to land plants. To construct this phylogenomic tree, the researchers sequenced 43 new transcriptome datasets for the Zygnematophyceae, establishing a phylodiverse dataset of 104 transcriptomes to examine genetic divergence across this species-rich streptophyte algal class.

Within the resulting phylogenomic tree, the analysis traces evolutionary divergence between the Spirogyrales and their unicellular sister group, the Desmidiales. Despite a deep split separating the Spirogyrales from the unicellular Desmidiales, the tree indicates that most Spirogyrales emerged after pronounced genetic divergence. According to the findings, this pronounced genetic divergence accommodated both the attainment of multicellularity and divergent traits such as unique cell division and plastid division. Overall, the transcriptome data capture signatures of massive ancient radiations across the Zygnematophyceae that could only be revealed through phylodiverse sampling.

All major phylogenomic efforts have concluded that the Zygnematophyceae are the algal sisters to land plants, an evolutionary placement that initially came as a surprise because of the algae’s plain body plans. Among streptophyte algae, the Zygnematophyceae constitute the class with the greatest species richness. However, while ample genome information was available for a few select members of zygnematophytes, understanding of genomic divergence and the genetic potential for key traits across the class remained limited by a lack of phylodiverse data accounting for that diversity within an integrated phylogenomic framework.

Because the closest streptophyte algal relatives of land plants, or embryophytes, hold key information on the last common ancestor of embryophytes and algae, discerning that ancestral nature allows researchers to retrace the adaptations that ushered in the conquest of land by plants. By addressing the lack of phylodiverse data where ample genome information covered only a few select zygnematophytes, this transcriptome-based phylogenomic framework documents a vast evolutionary history across the Zygnematophyceae. Recognizing both the deep genetic divergences and the vast evolutionary history of these streptophyte algae is key to illuminating the nature of the algal progenitors of land plants.

Subject of Research: Phylogenomic structure and evolutionary divergence of Zygnematophyceae streptophyte algae

Article Title: A deep genetic structure phylogenomically frames the closest algal relatives of land plants

Article References: Bierenbroodspot, M. J., Kunz, C. F., Goldbecker, E. S., Lorenz, M., Irisarri, I., Pröschold, T., Darienko, T., & de Vries, J. (2026). A deep genetic structure phylogenomically frames the closest algal relatives of land plants. PLOS Biology, 24(11), e3004005. https://doi.org/10.1371/journal.pbio.3004005

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004005

Keywords: Zygnematophyceae, phylogenomics, streptophyte algae, embryophytes, land plants, transcriptomes, Spirogyrales, Desmidiales, multicellularity, genetic divergence, deep, genetic