Transposable elements drive intron gain in diverse eukaryotes.

Area of Science:

• Genomics
• Evolutionary Biology
• Molecular Biology

Background:

• Intron number variation across eukaryotic genomes is significant, but evolutionary drivers are unclear.
• Intron gain and loss rates vary greatly among lineages, with some showing stasis and others rapid change.
• Specialized transposons, Introners, were recently discovered and hypothesized to drive intron gain, but their prevalence was unknown.

Purpose of the Study:

• To systematically search for Introners across a wide range of eukaryotic genomes.
• To determine the phylogenetic and ecological distribution of Introners.
• To investigate the evolutionary origins and mechanisms of Introners.

Main Methods:

• Conducted a large-scale genomic survey of 3,325 eukaryotic species.
• Identified Introner-derived introns using bioinformatic approaches.
• Analyzed phylogenetic and ecological data for species containing Introners.

Main Results:

• Identified 27,563 Introner-derived introns in 175 genomes (5.2% of surveyed species).
• Found Introners in phylogenetically diverse eukaryotes, including animals and basal protists, with a Last Common Ancestor over 1.7 billion years ago.
• Aquatic organisms were 6.5 times more likely to harbor Introners than terrestrial ones, and Introners showed mechanistic diversity consistent with convergent evolution from transposable elements.

Conclusions:

• Introners are a widespread source of intron creation across eukaryotic evolution.
• The distribution of Introners suggests horizontal gene transfer and aquatic environments may facilitate their spread.
• Introners likely explain the episodic and punctuated patterns of intron gain observed in eukaryotic genomes.