title: RNA Sequencing Revealed Numerous Polyketide Synthase Genes in the Harmful Dinoflagellate Karenia mikimotoi.
abstract: The dinoflagellate Karenia mikimotoi forms blooms in the coastal waters of temperate regions and occasionally causes massive fish and invertebrate mortality. This study aimed to elucidate the toxic effect of K. mikimotoi on marine organisms by using the genomics approach; RNA-sequence libraries were constructed, and data were analyzed to identify toxin-related genes. Next-generation sequencing produced 153,406 transcript contigs from the axenic culture of K. mikimotoi. BLASTX analysis against all assembled contigs revealed that 208 contigs were polyketide synthase (PKS) sequences. Thus, K. mikimotoi was thought to have several genes encoding PKS metabolites and to likely produce toxin-like polyketide molecules. Of all the sequences, approximately 30 encoded eight PKS genes, which were remarkably similar to those of Karenia brevis. Our phylogenetic analyses showed that these genes belonged to a new group of PKS type-I genes. Phylogenetic and active domain analyses showed that the amino acid sequence of four among eight Karenia PKS genes was not similar to any of the reported PKS genes. These PKS genes might possibly be associated with the synthesis of polyketide toxins produced by Karenia species. Further, a homology search revealed 10 contigs that were similar to a toxin gene responsible for the synthesis of saxitoxin (sxtA) in the toxic dinoflagellate Alexandrium fundyense. These contigs encoded A1-A3 domains of sxtA genes. Thus, this study identified some transcripts in K. mikimotoi that might be associated with several putative toxin-related genes. The findings of this study might help understand the mechanism of toxicity of K. mikimotoi and other dinoflagellates.
authors.affiliation: National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, Japan.|Research Fellow of the Japan Society for the Promotion of Science, Kojimachi Business Center Building, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Kimura
authors.affiliation: Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata, Japan.
authors.forename: Shujiro
authors.initials: S
authors.lastname: Okuda
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Nakayama
authors.affiliation: National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Shikata
authors.affiliation: Department of Biotechnology, College of Life Sciences, Rhitsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Takahashi
authors.affiliation: Laboratory of Aquatic Environmental Science, Faculty of Agriculture, Kochi University, 200, Monobe, Nankoku, Kochi, Japan.
authors.forename: Haruo
authors.initials: H
authors.lastname: Yamaguchi
authors.affiliation: National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, Japan.
authors.forename: Setsuko
authors.initials: S
authors.lastname: Skamoto
authors.affiliation: National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, Japan.
authors.forename: Mineo
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Tomaru
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D020451:Contig Mapping; D030541:Databases, Genetic; D004141:Dinoflagellida / Q000201:enzymology / Q000235:genetics*; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D048630:Polyketide Synthases / Q000737:chemistry / Q000235:genetics*; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012530:Saxitoxin / Q000737:chemistry; D017423:Sequence Analysis, RNA / Q000379:methods*; D017386:Sequence Homology, Amino Acid
chemical_list: D015800:Protozoan Proteins; D012530:Saxitoxin; D048630:Polyketide Synthases