Data_Sheet_1_Characterization of Iodine-Related Molecular Processes in the Marine Microalga Tisochrysis lutea (Haptophyta).DOCX

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 de novo transcriptome of Tisochrysis lutea 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- (aryl, ccp, perox, sod1, sod2, sod3, apx3, ahp1) and iodide-specific deiodinase (dio) genes increased their mRNA abundance progressively until the stationary phase to cope with oxidative stress. Moreover, the increase of dio mRNA abundance in aging cultures indicated that this enzyme was also involved in senescence. Cell treatments with iodide modified the expression of perox whereas treatments with iodate changed the transcript levels of gpx1 and ccp. To test the dependence of perox on iodide, microalgae cells were treated with hydrogen peroxide (H2O2) either in presence or absence of iodide observing that several genes related to reactive oxygen species (ROS) deactivation (perox, gpx1, apx2, apx3, ahp1, ahp2, sod1, sod3, and aryl) were transcriptionally activated although with some temporal differences. However, only the expression of perox was dependent on iodide levels indicating this enzyme, acquired by horizontal gene transfer (HGT), could act as a haloperoxidase. All these data indicate that T. lutea 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.

碘代谢对于海洋藻类的抗氧化防御作用以及碘的地球生物化学循环至关重要。此外，某些微藻能够合成类似甲状腺激素的化合物，这对于维持食物网至关重要。然而，关于微藻中碘相关分子过程的知识仍然相对匮乏。在本研究中，利用长读和短读数据组装了在高碘化物浓度（5 mM）下培养的黄色硅藻（Tisochrysis lutea）的从头转录组。建立了一个名为IsochrysisDB的数据库，以存储所有基因组信息。在微藻生长过程中的基因表达分析表明，大多数抗氧化（芳香族、ccp、过氧化氢酶、sod1、sod2、sod3、apx3、ahp1）和碘化物特异性脱碘酶（dio）基因在稳定期之前其mRNA丰度逐渐增加，以应对氧化应激。此外，老化培养中dio mRNA丰度的增加表明，该酶也参与了衰老过程。碘化物处理的细胞改变了过氧化氢酶的表达，而碘酸盐处理则改变了gpx1和ccp的转录水平。为了测试过氧化氢酶对碘化物的依赖性，微藻细胞在存在或不存在碘化物的情况下用过氧化氢（H2O2）处理，观察到与活性氧（ROS）失活相关的多个基因（过氧化氢酶、gpx1、apx2、apx3、ahp1、ahp2、sod1、sod3、和芳香族）在转录上被激活，尽管存在一些时间差异。然而，只有过氧化氢酶的表达依赖于碘化物水平，这表明通过水平基因转移（HGT）获得的该酶可以作为卤素过氧化物酶。所有这些数据表明，T. lutea通过协调激活抗氧化基因的表达来应对氧化应激。一个阶段调节的脱碘酶和一种新型卤素过氧化物酶的鉴定，为甲状腺信号传导的起源和进化以及碘在海洋环境中的抗氧化作用提供了新的线索。