AUTHOR=Hernández Javier Laura , Benzekri Hicham , Gut Marta , Claros M. Gonzalo , van Bergeijk Stefanie , Cañavate José Pedro , Manchado Manuel 

TITLE=Characterization of Iodine-Related Molecular Processes in the Marine Microalga Tisochrysis lutea (Haptophyta)

JOURNAL=Frontiers in Marine Science

VOLUME=5

YEAR=2018

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2018.00134

DOI=10.3389/fmars.2018.00134

ISSN=2296-7745

ABSTRACT=<p>Iodine metabolism is essential for the antioxidant defense of marine algae and in the biogeochemical cycle of iodine. Moreover, some microalgae can synthetize thyroid hormone-like compounds that are essential to sustain food webs. However, knowledge regarding iodine-related molecular processes in microalgae is still scarce. In this study, a <italic>de novo</italic> transcriptome of <italic>Tisochrysis lutea</italic> cultured under high iodide concentrations (5 mM) was assembled using both long and short reads. A database termed IsochrysisDB was established to host all genomic information. Gene expression analyses during microalgal growth showed that most of the antioxidant- (<italic>aryl, ccp, perox, sod1, sod2, sod3, apx3, ahp1</italic>) and iodide-specific deiodinase (<italic>dio</italic>) genes increased their mRNA abundance progressively until the stationary phase to cope with oxidative stress. Moreover, the increase of <italic>dio</italic> mRNA abundance in aging cultures indicated that this enzyme was also involved in senescence. Cell treatments with iodide modified the expression of <italic>perox</italic> whereas treatments with iodate changed the transcript levels of <italic>gpx1</italic> and <italic>ccp</italic>. To test the dependence of <italic>perox</italic> on iodide, microalgae cells were treated with hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) either in presence or absence of iodide observing that several genes related to reactive oxygen species (ROS) deactivation (<italic>perox, gpx1, apx2, apx3, ahp1, ahp2, sod1, sod3</italic>, and <italic>aryl</italic>) were transcriptionally activated although with some temporal differences. However, only the expression of <italic>perox</italic> was dependent on iodide levels indicating this enzyme, acquired by horizontal gene transfer (HGT), could act as a haloperoxidase. All these data indicate that <italic>T. lutea</italic> activates coordinately the expression of antioxidant genes to cope with oxidative stress. The identification of a phase-regulated deiodinase and a novel haloperoxidase provide new clues about the origin and evolution of thyroid signaling and the antioxidant role of iodine in the marine environment.</p>