AUTHOR=Mendoza-Flores Armando , Leyva-Valencia Ignacio , Band-Schmidt Christine J. , Galindo-Sánchez Clara E. , Bustillos-Guzmán José J. 

TITLE=Identification of the Gene sxtA (Domains sxtA1 and sxtA4) in Mexican Strains of Gymnodinium catenatum (Dinophyceae) and Their Evolution

JOURNAL=Frontiers in Marine Science

VOLUME=5

YEAR=2018

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2018.00289

DOI=10.3389/fmars.2018.00289

ISSN=2296-7745

ABSTRACT=<p>Saxitoxin (STX) and its analogs are a broad group of natural neurotoxic alkaloids, commonly known as paralytic shellfish toxins. <italic>SxtA</italic> is the initial gene in the biosynthesis of saxitoxin. It has been proposed that the genes for STX biosynthesis had a bacterial origin and were acquired in the dinoflagellates by a horizontal gene transfer (HGT). In <italic>Gymnodinium catenatum</italic>, the origin of the STX genes is not well established. In this paper, we sequenced <italic>sxtA</italic> gene (domains <italic>sxtA1</italic> and <italic>sxtA4</italic>) and determined the gene copy number in the genome in four Mexican strains of <italic>G. catenatum</italic>. We compare them with sequences of <italic>G. catenatum, Pyrodinium bahamense</italic>, and <italic>Alexandrium</italic> spp. from other geographic regions, and non-toxic producing dinoflagellates. Amplifications were performed for domains <italic>sxtA1</italic> and <italic>sxtA4</italic> from strains of <italic>G. catenatum</italic> and the phylogenetic analyses was done by maximum likelihood and Bayesian inference. The copy number determination was carried out using qPCR. The phylogenetic tree of domain <italic>sxtA4</italic> showed the formation of two clades where <italic>G. catenatum</italic> sequences separated from the <italic>Alexandrium/Pyrodinium</italic> clade. The domain <italic>sxtA1</italic> formed a higher number of clades than <italic>sxtA4</italic>. Sequences of <italic>G. catenatum</italic> were grouped together with sequences of <italic>Alexandrium</italic>. Dinoflagellates sequences that do not produce saxitoxin formed a separate clade. The gene copy number was 64 ± 30 and 110 ± 50 copies of <italic>sxtA1</italic> and <italic>sxtA4</italic> respectively. The identification of the gene <italic>sxtA</italic> of <italic>G. catenatum</italic> shows that the sequences are similar to those of <italic>Alexandrium</italic> species with low variations between species. These results may indicate that the acquisition of the gene <italic>sxtA</italic> was an early HGT event in the evolution of dinoflagellates. The possible loss of the ability to produce STX in some species suggests that the HGT from <italic>Alexandrium</italic> species toward <italic>G. catenatum</italic> is not possible.</p>