title: Gene expression and molecular evolution of sxtA4 in a saxitoxin producing dinoflagellate Alexandrium catenella.
abstract: Dinoflagellates of the genus Alexandrium produce the neurotoxin saxitoxin (STX), responsible for paralytic shellfish poisoning (PSP) and accumulates in marine invertebrates. The recent identification of STX biosynthesis genes allowed us to investigate the expression of sxtA4 at different growth stages in Alexandrium catenella Group IV. We found no significant differences in expression of sxtA4, despite significant differences in STX levels at different growth stages (P < 0.023). Three reference genes were tested for normalisation: actin, cytochrome b (cob), and the large subunit ribosomal RNA (LSU rDNA). cob was most stably expressed but the combination of two reference genes, actin and cob, resulted in the best stability factor. Most genomic sequences of sxtA4 from A. catenella were in a clade that included sequences from Alexandrium fundyense Group I, however, one paralogue was not related to the others, suggesting recombination or lateral transfer. A comparison of the sxtA4 cDNA sequences with genomic DNA sequences indicated the possibility of transcript editing and the preferential transcription of certain genomic DNA loci. The results show that, in dinoflagellates, post-transcriptional mechanisms play a major role in the regulation of saxitoxin biosynthesis.
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia; Sydney Institute of Marine Science, Chowder Bay Rd, Mosman, NSW 2088, Australia. Electronic address: wiese.maria123@gmail.com.
authors.forename: Maria
authors.initials: M
authors.lastname: Wiese
authors.affiliation: Sydney Institute of Marine Science, Chowder Bay Rd, Mosman, NSW 2088, Australia; Plant Functional Biology and Climate Change Cluster, University of Technology, Sydney, NSW 2007, Australia.
authors.forename: Shauna A
authors.initials: SA
authors.lastname: Murray
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Alfonsus
authors.initials: A
authors.lastname: Alvin
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia; Sydney Institute of Marine Science, Chowder Bay Rd, Mosman, NSW 2088, Australia. Electronic address: b.neilan@unsw.edu.au.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Neilan
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001499:Bayes Theorem; D003001:Cloning, Molecular; D045303:Cytochromes b / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004141:Dinoflagellida / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009517:New South Wales; D010802:Phylogeny; D054658:Ribosome Subunits, Large / Q000235:genetics / Q000378:metabolism; D012530:Saxitoxin / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D000199:Actins; D017931:DNA Primers; D018076:DNA, Complementary; D012530:Saxitoxin; D045303:Cytochromes b
keywords: Alexandrium; Dinoflagellates; Gene expression; Real-time quantitative PCR; Reference genes; Saxitoxin