<em>Symbiodinium</em> Transcriptomes: Genome Insights into the Dinoflagellate Symbionts of Reef-Building Corals

<div><p>Dinoflagellates are unicellular algae that are ubiquitously abundant in aquatic environments. Species of the genus <em>Symbiodinium</em> form symbiotic relationships with reef-building corals and other marine invertebrates. Despite their ecologic importance, little is known about the genetics of dinoflagellates in general and <em>Symbiodinium</em> in particular. Here, we used 454 sequencing to generate transcriptome data from two <em>Symbiodinium</em> species from different clades (clade A and clade B). With more than 56,000 assembled sequences per species, these data represent the largest transcriptomic resource for dinoflagellates to date. Our results corroborate previous observations that dinoflagellates possess the complete nucleosome machinery. We found a complete set of core histones as well as several H3 variants and H2A.Z in one species. Furthermore, transcriptome analysis points toward a low number of transcription factors in <em>Symbiodinium</em> spp. that also differ in the distribution of DNA-binding domains relative to other eukaryotes. In particular the cold shock domain was predominant among transcription factors. Additionally, we found a high number of antioxidative genes in comparison to non-symbiotic but evolutionary related organisms. These findings might be of relevance in the context of the role that <em>Symbiodinium</em> spp. play as coral symbionts.</p> <p>Our data represent the most comprehensive dinoflagellate EST data set to date. This study provides a comprehensive resource to further analyze the genetic makeup, metabolic capacities, and gene repertoire of <em>Symbiodinium</em> and dinoflagellates. Overall, our findings indicate that <em>Symbiodinium</em> possesses some unique characteristics, in particular the transcriptional regulation in <em>Symbiodinium</em> may differ from the currently known mechanisms of eukaryotic gene regulation.</p>