title: Intron Invasions Trace Algal Speciation and Reveal Nearly Identical Arctic and Antarctic Micromonas Populations.
abstract: Spliceosomal introns are a hallmark of eukaryotic genes that are hypothesized to play important roles in genome evolution but have poorly understood origins. Although most introns lack sequence homology to each other, new families of spliceosomal introns that are repeated hundreds of times in individual genomes have recently been discovered in a few organisms. The prevalence and conservation of these introner elements (IEs) or introner-like elements in other taxa, as well as their evolutionary relationships to regular spliceosomal introns, are still unknown. Here, we systematically investigate introns in the widespread marine green alga Micromonas and report new families of IEs, numerous intron presence-absence polymorphisms, and potential intron insertion hot-spots. The new families enabled identification of conserved IE secondary structure features and establishment of a novel general model for repetitive intron proliferation across genomes. Despite shared secondary structure, the IE families from each Micromonas lineage bear no obvious sequence similarity to those in the other lineages, suggesting that their appearance is intimately linked with the process of speciation. Two of the new IE families come from an Arctic culture (Micromonas Clade E2) isolated from a polar region where abundance of this alga is increasing due to climate induced changes. The same two families were detected in metagenomic data from Antarctica--a system where Micromonas has never before been reported. Strikingly high identity between the Arctic isolate and Antarctic coding sequences that flank the IEs suggests connectivity between populations in the two polar systems that we postulate occurs through deep-sea currents. Recovery of Clade E2 sequences in North Atlantic Deep Waters beneath the Gulf Stream supports this hypothesis. Our research illuminates the dynamic relationships between an unusual class of repetitive introns, genome evolution, speciation, and global distribution of this sentinel marine alga.
authors.affiliation: Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA Department of Ocean Sciences, University of California Santa Cruz.
authors.forename: Melinda P
authors.initials: MP
authors.lastname: Simmons
authors.affiliation: Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA.
authors.forename: Charles
authors.initials: C
authors.lastname: Bachy
authors.affiliation: Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Sudek
authors.affiliation: Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA.
authors.forename: Marijke J
authors.initials: MJ
authors.lastname: van Baren
authors.affiliation: Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Sudek
authors.affiliation: Department of Molecular, Cell & Developmental Biology, University of California Santa Cruz.
authors.forename: Manuel
authors.initials: M
authors.lastname: Ares
authors.affiliation: Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA Department of Ocean Sciences, University of California Santa Cruz Integrated Microbial Biodiversity Program, Canadian Institute for Advanced Research, Toronto, ON, Canada azworden@mbari.org.
authors.forename: Alexandra Z
authors.initials: AZ
authors.lastname: Worden
mesh_terms: D000864:Antarctic Regions; D001110:Arctic Regions; D001483:Base Sequence; D000460:Chlorophyta / Q000235:genetics*; D017343:Genes, Plant; D049810:Genetic Speciation; D007438:Introns; D055029:Inverted Repeat Sequences; D008969:Molecular Sequence Data; D058974:Phylogeography; D010839:Phytoplankton / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D012337:RNA, Ribosomal, 18S; D017423:Sequence Analysis, RNA
chemical_list: D018749:RNA, Plant; D012337:RNA, Ribosomal, 18S
keywords: Introner Elements; introns; marine algae; phytoplankton; polar systems; repetitive introns