Multiple group I introns detected in the nuclear small subunit rDNA of the autosporic green alga Selenastrum capricornutum

A phylogenetic investigation of the autosporic chlorophycean alga species Selenastrum capricornutum using the small subunit (SSU) rRNA gene revealed the unusual presence of six group IC1 introns. Previous studies showed that numerous green algal taxa contain group IC1 introns. However, whereas some algal species harbor multiple introns in a single ribosomal gene, none have contained as many as S. capricornutum. Three of the S. capricornutum introns are located at conserved algal intron sites and the remaining three are located at novel eukaryotic positions. The SSU rRNA genes and their introns have been sequenced and putative secondary structures are proposed for the introns. Also, their similarity to other group IC1 introns from algal, fungal, and viral sources is investigated. Results suggest the initial presence of introns at conserved locations, followed by duplication and insertion to novel positions within the SSU rRNA gene.