Nucleomorph phylogenomics suggests a deep and ancient origin of cryptophyte plastids within Rhodophyta

Area of Science:

• * Evolutionary biology
• * Molecular phylogenetics
• * Algal genomics

Background:

• * The evolutionary history of complex plastids in eukaryotes, specifically those derived from red algae, is not fully understood.
• * Cryptophyta harbors complex plastids and retains nucleomorphs, which are reduced red algal nuclei containing genes.
• * Nucleomorph genes offer a unique dataset for phylogenomic analysis, independent of plastid-encoded genes.

Purpose of the Study:

• * To reconstruct the evolutionary origin of red algae-derived complex plastids using cryptophyte nucleomorph genes.
• * To determine the phylogenetic position of cryptophyte nucleomorphs within the red algae (Rhodophyta).
• * To provide phylogenomic data independent of plastid-encoded proteins.

Main Methods:

• * Performed phylogenomic analysis using genes from cryptophyte nucleomorphs.
• * Included sequence data from seven deep-branching red algae.
• * Employed rigorous topology tests to support phylogenetic inferences.

Main Results:

• * Cryptophyte nucleomorphs were phylogenetically placed as sister to the Cyanidiophytina subphylum.
• * This finding contradicts previous studies that positioned red complex plastids closer to Rhodophytina based on plastidial genes.
• * The analysis rejected an origin of nucleomorphs from within currently recognized Rhodophyta classes.

Conclusions:

• * Cryptophyte nucleomorphs likely originated from an ancient lineage at the base of the red algal tree of life.
• * The precise sister group to cryptophyte nucleomorphs requires further investigation.
• * Complex red plastids likely have a deep evolutionary origin within Rhodophyta.