Contrasting modes of intron evolution in an evolutionarily distinct eukaryotic lineage revealed by comparative genomics of ciliated protists.

Deep-branching ciliates experienced massive intron loss and show a dominance of tiny 3n introns, contrasting with derived ciliates' more uniform intron distribution.

• Why it matters: Understanding intron evolution in ancient unicellular eukaryotes like ciliates fills a knowledge gap about genome evolution mechanisms in early-diverging lineages, which may differ from well-studied multicellular organisms.
• What they did: Using a newly sequenced high-quality genome and comparative genomics of derived and deep-branching ciliates, the study analyzed intron patterns, spliceosome components, and whole-genome duplications, including 27,571 protein-coding genes in Blepharisma.
• The result: Findings suggest that deep-branching ciliates' introns are retained to facilitate nonsense-mediated decay, and lineage-specific splicing regulation varies, providing new insights into unconventional intron evolutionary strategies in unicellular eukaryotes.