The symbiosis between corals and dinoflagellates in the family Symbiodiniaceae is threatened by warming trends that induce coral bleaching, or symbiosis breakdown. Current models of symbiosis breakdown involve an immune response to an elevation in reactive oxygen species that ultimately results in the loss of the symbiont. However, the intimate nature of the symbiosis implies an important role for the symbiont surface as a point of interaction between partners. The response of symbiont cell surface proteins to experimental temperature stress was, therefore, investigated using a cell surface biotin probe. Cell-surface protein composition was found to be dynamically regulated in response to heat stress, particularly after 24 h of exposure to heat treatment. This pattern was primarily driven by an increased abundance in heat shock proteins, demonstrating that stress experienced by the symbiont can manifest at the cell surface. Elements known to activate host immunity were also increased in response to temperature stress, further demonstrating an avenue by which the symbiont can elicit a host immune response independent of reactive oxygen species. This work documents the cell surface protein composition of a Symbiodiniaceae species for the first time and highlights host–symbiont interaction mechanisms that may be important during symbiosis breakdown.

中文翻译：

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珊瑚共生体 Breviolum psygmophilum 的细胞表面蛋白质组成揭示了宿主特异性的机制，并在温度胁迫期间显示出动态调节

共生科珊瑚和甲藻之间的共生受到导致珊瑚白化或共生破坏的变暖趋势的威胁。当前的共生破坏模型涉及对活性氧升高的免疫反应，最终导致共生体的丧失。然而，共生的亲密性质意味着共生表面作为伙伴之间相互作用的一个点的重要作用。因此，使用细胞表面生物素探针研究了共生体细胞表面蛋白对实验温度应激的反应。发现细胞表面蛋白质组成响应热应激而动态调节，特别是在暴露于热处理 24 小时后。这种模式主要是由热休克蛋白丰度增加驱动的，证明共生体经历的压力可以在细胞表面表现出来。已知激活宿主免疫的元素也随着温度应激而增加，进一步证明了共生体可以引发宿主免疫反应的途径，而不受活性氧的影响。这项工作首次记录了共生科物种的细胞表面蛋白质组成，并强调了在共生分解过程中可能很重要的宿主-共生体相互作用机制。