Toxic dinoflagellates belonging to the genus Dinophysis acquire plastids indirectly from cryptophytes through the consumption of the ciliate Mesodinium rubrum . Dinophysis acuminata harbours three genes encoding plastid-related proteins, which are thought to have originated from fucoxanthin dinoflagellates, haptophytes and cryptophytes via lateral gene transfer (LGT). Here, we investigate the origin of these plastid proteins via RNA sequencing of species related to D. fortii . We identified 58 gene products involved in porphyrin, chlorophyll, isoprenoid and carotenoid biosyntheses as well as in photosynthesis. Phylogenetic analysis revealed that the genes associated with chlorophyll and carotenoid biosyntheses and photosynthesis originated from fucoxanthin dinoflagellates, haptophytes, chlorarachniophytes, cyanobacteria and cryptophytes. Furthermore, nine genes were laterally transferred from fucoxanthin dinoflagellates, whose plastids were derived from haptophytes. Notably, transcription levels of different plastid protein isoforms varied significantly. Based on these findings, we put forth a novel hypothesis regarding the evolution of Dinophysis plastids that ancestral Dinophysis species acquired plastids from haptophytes or fucoxanthin dinoflagellates, whereas LGT from cryptophytes occurred more recently. Therefore, the evolutionary convergence of genes following LGT may be unlikely in most cases.

Diatoms are one of the most prominent oceanic primary producers and are now recognized to be distributed throughout the world. They maintain their population despite predators, infections, and unfavourable environmental conditions. One of the smallest diatoms, Chaetoceros tenuissimus, can coexist with infectious viruses during blooms. To further understand this relationship, we sequenced the C. tenuissimus strain NIES-3715 genome. A gene fragment of a replication-associated gene from the infectious ssDNA virus (designated endogenous virus-like fragment, EVLF) was found to be integrated into each 41 Mb of haploid assembly. In addition, the EVLF was transcriptionally active and conserved in nine other C. tenuissimus strains from different geographical areas, although the primary structures of their proteins varied. The phylogenetic tree further suggested that the EVLF was acquired by the ancestor of C. tenuissimus. Additionally, retrotransposon genes possessing a reverse transcriptase function were more abundant in C. tenuissimus than in Thalassiosira pseudonana and Phaeodactylum tricornutum. Moreover, a target site duplication, a hallmark for long interspersed nuclear element retrotransposons, flanked the EVLF. Therefore, the EVLF was likely integrated by a retrotransposon during viral infection. The present study provides further insights into the diatom-virus evolutionary relationship.

Heliopora coerulea is the only species in the subclass Octocorallia that has a crystalline aragonite skeleton. The skeleton has been reported to contain the blue pigment, biliverdin IXα, which is formed by heme oxygenase (HO) during heme decomposition. There is little information regarding gene expression in H. coerulea; therefore, the biosynthesis pathway for biliverdin IXα is poorly understood. To identify the genes related to heme synthesis and degradation, metatranscripts of H. coerulea and its symbiont Symbiodinium spp. were sequenced and separated from the host- and symbiont-derived sequences. From the metatranscriptome analyses, all genes for heme synthesis and three HOs were isolated from the host and symbiont. From our phylogenetic and amino acid analysis, we noted that one of the HO isoforms in the host coral was predicted to possess HO activity. However, biliverdin reductase, which reduces biliverdin to bilirubin, was not identified in the present study. Similarly, biliverdin reductase was not identified in the transcripts of the red coral Corallium rubrum, a species that also belongs to Octocorallia. However, genes related to heme synthesis and HO were found in C. rubrum. We speculate that Heliopora coerulea can produce biliverdin and accumulate it in the skeleton, while red corals and other Octocorallia species cannot. Further information from molecular studies of H. coerulea will provide insights into the synthesis of biliverdin IXα, the blue pigment in the hard crystalline aragonite skeleton, and will be fundamental to future ecological and physiological studies.

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A B S T R A C TSince 2002, blooms of Alexandrium catenella sensu Fraga et al. (2015) and paralytic shellfish toxicity events have occurred almost yearly in Osaka Bay, Japan. To better understand the triggers for reoccurring A. catenella blooms in Osaka Bay, phytoplankton community was monitored during the spring seasons of 2012-2015. Monitoring was performed using massively parallel sequencing (MPS)-based technique on amplicon sequences of the 18S rRNA gene. Dense blooms of A. catenella occurred every year except in 2012, however, there was no significant correlation with the environmental parameters investigated. Plankton community diversity decreased before and middle of the A. catenella blooms, suggesting that the decline in diversity could be an indicator for the bloom occurrence. The yearly abundance pattern of A. catenella cells obtained by morphology-based counting coincided with the relative sequence abundances, which supports the effectiveness of MPS-based phytoplankton monitoring.

, and is assumed to facilitate inorganic carbon (C i ) uptake and transport to the symbiont. However, the localization of CA in gill tissue remains unknown. We therefore analyzed mRNA sequences, proteins and CA activity in Calyptogena okutanii using expression sequence tag, SDS-PAGE and LC-MS/MS. We found that acetazolamide-sensitive soluble CA was abundantly expressed in the gill tissue of C. okutanii, and the enzyme was purified by affinity chromatography. Mouse monoclonal antibodies against the CA of C. okutanii were used in western blot analysis and immunofluorescence staining of the gill tissues of C. okutanii, which showed that CA was exclusively localized in the symbiont-harboring cells (bacteriocytes) in gill epithelial cells. Western blot analysis and measurement of activity showed that CA was abundantly (26-72% of total soluble protein) detected in the gill tissues of not only Calyptogena clams but also deep-sea Bathymodiolus mussels that harbor thioautotrophic or methanotrophic symbiotic bacteria, but was not detected in a non-symbiotic mussel, Mytilus sp. The present study showed that CA is abundant in the gill tissues of deep-sea symbiotic bivalves and specifically localizes in the cytoplasm of bacteriocytes of C. okutanii. This indicates that the C i supply process to symbionts in the vacuole (symbiosome) in bacteriocytes is essential for symbiosis. Supplementary material available online at

Currently, no tool is available that precisely identifies and quantifies all 48 species of Pseudo-nitzschia simultaneously. In the present study, we used massively parallel sequencing-based technology with genus-specific Pseudo-nitzschia primers to investigate the distribution and population dynamics of the genus in Tokyo Bay, Japan. Furthermore, we attempted to quantify the abundance of each species using both relative abundance data detected in the massively parallel sequencing-based survey, and cell count data, obtained by light microscopy. Several species of Pseudo-nitzschia were detected continuously from July 10 to September 9, 2016 in the sampling location. Cell densities ranged from 2-300 cells mL −1 (sample no.=10). Fourteen operational taxonomic units (OTUs) attributable to Pseudonitzschia were detected, and 99.9% of sequences detected by massively parallel sequencing belonged to the genus. Each of the most abundant OTUs comprised a single species, and were identified, in decreasing order of abundance, as P. multistriata (Takano) Takano, P. pungens (Grunow ex Cleve) Hasle, P. fraudulenta (Cleve) Hasle, P. multiseries (Hasle) Hasle, and P. galaxiae Lundholm & Moestrup. Species identification was possible in 9 of the 14 OTUs detected, of which several were detected in Tokyo Bay for the first time. The cell abundance ranges of the five most abundant species were estimated as 1, 976-246,395, 0.03-52,999, 5-42,820, 4-24,617, and 0.03-1,007 cells L −1 , respectively. The detection limit was 0.03 cells L −1.