Category: Dinoflagellate genomics

Unfolding the secrets of coral-algal symbiosis.

ISME J. 2014 Oct 24;

Authors: Rosic N, Ling EY, Chan CK, Lee HC, Kaniewska P, Edwards D, Dove S, Hoegh-Guldberg O

Abstract
Dinoflagellates from the genus Symbiodinium form a mutualistic symbiotic relationship with reef-building corals. Here we applied massively parallel Illumina sequencing to assess genetic similarity and diversity among four phylogenetically diverse dinoflagellate clades (A, B, C and D) that are commonly associated with corals. We obtained more than 30 000 predicted genes for each Symbiodinium clade, with a majority of the aligned transcripts corresponding to sequence data sets of symbiotic dinoflagellates and <2% of sequences having bacterial or other foreign origin. We report 1053 genes, orthologous among four Symbiodinium clades, that share a high level of sequence identity to known proteins from the SwissProt (SP) database. Approximately 80% of the transcripts aligning to the 1053 SP genes were unique to Symbiodinium species and did not align to other dinoflagellates and unrelated eukaryotic transcriptomes/genomes. Six pathways were common to all four Symbiodinium clades including the phosphatidylinositol signaling system and inositol phosphate metabolism pathways. The list of Symbiodinium transcripts common to all four clades included conserved genes such as heat shock proteins (Hsp70 and Hsp90), calmodulin, actin and tubulin, several ribosomal, photosynthetic and cytochrome genes and chloroplast-based heme-containing cytochrome P450, involved in the biosynthesis of xanthophylls. Antioxidant genes, which are important in stress responses, were also preserved, as were a number of calcium-dependent and calcium/calmodulin-dependent protein kinases that may play a role in the establishment of symbiosis. Our findings disclose new knowledge about the genetic uniqueness of symbiotic dinoflagellates and provide a list of homologous genes important for the foundation of coral-algal symbiosis.The ISME Journal advance online publication, 24 October 2014; doi:10.1038/ismej.2014.182.

PMID: 25343511 [PubMed – as supplied by publisher]

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Are Niemann-Pick type C proteins key players in cnidarian-dinoflagellate endosymbioses?

Mol Ecol. 2014 Sep;23(18):4527-40

Authors: Dani V, Ganot P, Priouzeau F, Furla P, Sabourault C

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The symbiotic interaction between cnidarians, such as corals and sea anemones, and the unicellular algae Symbiodinium is regulated by yet poorly understood cellular mechanisms, despite the ecological importance of coral reefs. These mechanisms, including host-symbiont recognition and metabolic exchange, control symbiosis stability under normal conditions, but also lead to symbiosis breakdown (bleaching) during stress. This study describes the repertoire of the sterol-trafficking proteins Niemann-Pick type C (NPC1 and NPC2) in the symbiotic sea anemone Anemonia viridis. We found one NPC1 gene in contrast to the two genes (NPC1 and NPC1L1) present in vertebrate genomes. While only one NPC2 gene is present in many metazoans, this gene has been duplicated in cnidarians, and we detected four NPC2 genes in A. viridis. However, only one gene (AvNPC2-d) was upregulated in symbiotic relative to aposymbiotic sea anemones and displayed higher expression in the gastrodermis (symbiont-containing tissue) than in the epidermis. We performed immunolabelling experiments on tentacle cross sections and demonstrated that the AvNPC2-d protein was closely associated with symbiosomes. In addition, AvNPC1 and AvNPC2-d gene expression was strongly downregulated during stress. These data suggest that AvNPC2-d is involved in both the stability and dysfunction of cnidarian-dinoflagellate symbioses.

PMID: 25066219 [PubMed – in process]

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Genomic Insights in Processes Driving the Infection of Alexandrium tamarense by the Parasitoid Amoebophrya sp.

Eukaryot Cell. 2014 Sep 19;

Authors: Lu Y, Wohlrab S, Glöckner G, Guillou L, John U

Abstract
The regulatory circuits during infection of dinoflagellates by their parasites are largely unknown on the molecular level. Here we provide molecular insights into these infection dynamics. Alexandrium tamarense is one of the most prominent Harmful Algal Bloom dinoflagellate. Its pathogen, the dinoflagellate parasitoid Amoebophrya spp., has been observed to infect and control the blooms of this species. We generated a dataset of transcripts from three time points during the infection of this parasite-host system (0, 6 and 96 hours). Assembly of all transcript data from the parasitoid (>900.000 reads/313MBp with 454/Roche NGS) yielded 14,455 contigs, to which we mapped the raw transcript reads of each time point of the infection cycle. We show that particular surface lectins are expressed at the beginning of the infection cycle, which likely mediate the attachment to the host cell. In a later phase signal transduction related genes together with transmembrane transport and cytoskeleton proteins point to a high integration of processes involved in host recognition, adhesion, and invasion. At the final maturation stage, cell division and proliferation related genes were highly expressed, reflecting the fast cell growth and nuclear division of the parasitoid. Our molecular insights in dinoflagellate parasitoid interaction point to general mechanisms also known from other eukaryotic parasites, especially from the Alveolata. These similarities indicate the presence of fundamental processes of parasitoid infection that have remained stable throughout evolution within different phyla.

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