Cnidarians cannot synthesize sterols (which play essential roles in growth and development) de novo but often use sterols acquired from endosymbiotic dinoflagellates. While sterol availability can impact the mutualistic interaction between coral host and algal symbiont, the biosynthetic pathways (in the dinoflagellate endosymbionts) and functional roles of sterols in these symbioses are poorly understood. In this study, we found that itraconazole, which perturbs sterol metabolism by inhibiting the sterol 14-demethylase CYP51 in dinoflagellates, induces bleaching of the anemone Heteractis crispa and that bleaching perturbs sterol metabolism of the dinoflagellate. While Symbiodiniaceae have clade-specific sterol metabolites, they share features of the common sterol biosynthetic pathway but with distinct architecture and substrate specificity features of participating enzymes. Tracking sterol profiles and transcripts of enzymes involved in sterol biosynthesis across time in response to different environmental cues revealed similarities and idiosyncratic features of sterol synthesis in the endosymbiont Breviolum minutum. Exposure of algal cultures to high levels of light, heat, and acidification led to alterations in sterol synthesis, including blocks through downregulation of squalene synthase transcript levels accompanied by marked growth reductions.

中文翻译：

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甲藻内共生体中进化枝特异性甾醇代谢物与响应环境信号的珊瑚白化有关

刺胞动物不能从头合成甾醇（在生长和发育中发挥重要作用），但经常使用从内共生甲藻获得的甾醇。虽然甾醇的可用性可以影响珊瑚宿主和藻类共生体之间的互利相互作用，但人们对甾醇在这些共生体中的生物合成途径（在甲藻内共生体中）和功能作用知之甚少。在这项研究中，我们发现伊曲康唑通过抑制甲藻中的甾醇 14-脱甲基酶 CYP51 来扰乱甾醇代谢，从而诱导海葵Heteractis Cripa漂白，并且漂白扰乱了甲藻的甾醇代谢。虽然共生藻科具有进化枝特异性甾醇代谢物，但它们具有常见甾醇生物合成途径的特征，但具有不同的结构和参与酶的底物特异性特征。跟踪不同时间响应不同环境线索的甾醇生物合成所涉及的酶的甾醇谱和转录本揭示了内共生体短短孢菌中甾醇合成的相似性和特殊特征。将藻类培养物暴露于高水平的光、热和酸化会导致甾醇合成的改变，包括通过下调角鲨烯合酶转录水平而导致的阻断，并伴随着明显的生长减少。