Dimethylsulfoniopropionate, superoxide dismutase and glutathione as stress response indicators in three corals under short-term hyposalinity stress

Corals are among the most active producers of dimethylsulfoniopropionate (DMSP), a key molecule in marine sulfur cycling, yet the specific physiological role of DMSP in corals remains elusive. Here, we examine the oxidative stress response of three coral species (Acropora millepora, Stylophora pistillata and Pocillopora damicornis) and explore the antioxidant role of DMSP and its breakdown products under short-term hyposalinity stress. Symbiont photosynthetic activity declined with hyposalinity exposure in all three reef-building corals. This corresponded with the upregulation of superoxide dismutase and glutathione in the animal host of all three species. For the symbiont component, there were differences in antioxidant regulation, demonstrating differential responses to oxidative stress between the Symbiodinium subclades. Of the three coral species investigated, only A. millepora provided any evidence of the role of DMSP in the oxidative stress response. Our study reveals variability in antioxidant regulation in corals and highlights the influence life-history traits, and the subcladal differences can have on coral physiology. Our data expand on the emerging understanding of the role of DMSP in coral stress regulation and emphasizes the importance of exploring both the host and symbiont responses for defining the threshold of the coral holobiont to hyposalinity stress.

珊瑚是二甲基巯基丙酸内盐（dimethylsulfoniopropionate，DMSP）的主要产生者之一，该物质是海洋硫循环中的关键分子，但DMSP在珊瑚体内的具体生理功能仍尚不明确。本研究针对三种造礁珊瑚（微孔鹿角珊瑚*Acropora millepora*、指形松枝珊瑚*Stylopora pistillata*以及多孔鹿角珊瑚*Pocillopora damicornis*）的氧化应激（oxidative stress）响应展开分析，并探究了DMSP及其降解产物在短期低盐胁迫（hyposalinity stress）下的抗氧化作用。三种造礁珊瑚的共生藻光合活性均随低盐胁迫暴露时间延长而下降，这与三种珊瑚宿主体内超氧化物歧化酶（superoxide dismutase）与谷胱甘肽（glutathione）的表达上调相一致。对于共生藻组分而言，其抗氧化调控存在差异，表明不同虫黄藻亚支系（Symbiodinium subclades）对氧化应激的响应各不相同。在所研究的三种珊瑚物种中，仅微孔鹿角珊瑚（*A. millepora*）存在DMSP参与氧化应激响应的相关证据。本研究揭示了珊瑚体内抗氧化调控的多样性，并强调了生活史特征以及虫黄藻亚支系差异对珊瑚生理功能的影响。本研究的数据拓展了学界对DMSP在珊瑚胁迫调控中作用的新兴认知，并强调了同时探究宿主与共生藻的响应，对于明确珊瑚全息体（coral holobiont）耐受低盐胁迫的阈值具有重要意义。