Introner Elements Persist in Algal and Protist Species
Engineering
Corbett Lab
Introns are sequences interrupting genes that must be removed from mRNA before translation, and are a hallmark of eukaryotic genomes. They likely play important roles in genome evolution, but have poorly understood origins (Simmons et al. 2015). Many species exhibit major intron loss events, which probably occur through RNA mediated homologous recombination of cDNA (Lee and Stevens 2016). In contrast, some species exhibit prolific intron gain. Micromonas pusilla, an aquatic picophytoplankton, probably exhibits the most notable recent case of intron gain. Intronic sequences known as introner elements (IEs) colonized the M. pusilla genome in astounding quantities, likely through a mechanism involving DNA transposition (Huff et al. 2016). Contrary to canonical introns, introner elements exhibit conserved sequences and lengths. Similar phenomena are known to exist in fungi (van der Burgt et al 2012; Wu et al. 2017). We developed a computational pipeline for introner element detection and employed it on 1113 algal and protist assemblies. We report novel IE discoveries in 6 species, suggesting that IE invasions are more widespread than previously thought. IE families in closely related species do not share sequence similarity, indicating that they may have evolved independently. Perhaps intron gain is a fundamental driver of genome structure evolution.
