Chen Ching-Nen Nathan, Yong Tze Ching, Wang Jih-Terng
Department of Oceanography, National Sun Yat-Sen University, Kaohsiung, 804, Taiwan.
Bot Stud. 2025 Jan 15;66(1):3. doi: 10.1186/s40529-025-00451-5.
Large-scale coral bleaching events have become increasingly frequent in recent years. This process occurs when corals are exposed to high temperatures and intense light stress, leading to an overproduction of reactive oxygen species (ROS) by their endosymbiotic dinoflagellates. The ROS buildup prompts corals to expel these symbiotic microalgae, resulting in the corals' discoloration. Reducing ROS production and enhancing detoxification processes in these microalgae are crucial to prevent the collapse of coral reef ecosystems. However, research into the cell physiology and genetics of coral symbiotic dinoflagellates has been hindered by challenges associated with cloning these microalgae.
A procedure for cloning coral symbiotic dinoflagellates was developed in this study. Several species of coral symbionts were successfully cloned, with two of them further characterized. Experiments with the two species isolated from Turbinaria sp. showed that damage from light intensity at 340 μmol photons/m/s was more severe than from high temperature at 36 °C. Additionally, preincubation in high salinity conditions activated their endogenous tolerance to bleaching stress. Pretreatment at 50 ppt salinity reduced the percentage of cells stained for ROS by 59% and 64% in the two species under bleaching stress compared to those incubated at 30 ppt. Furthermore, their Fv'/Fm' during the recovery period showed a significant improvement compared to the controls.
These findings suggest that intense light plays a more important role than high temperatures in coral bleaching by enhancing ROS generation in the symbiotic dinoflagellates. The findings also suggest the genomes of coral symbiotic dinoflagellates have undergone evolutionary processes to develop mechanisms, regulated by gene expression, to mitigate damages caused by high temperature and high light stress. Understanding this gene expression regulation could contribute to strengthening corals' resilience against the impact of global climate change.
近年来，大规模珊瑚白化事件愈发频繁。当珊瑚暴露于高温和强光胁迫下时，就会发生这一过程，导致其共生的甲藻产生过量活性氧（ROS）。ROS的积累促使珊瑚排出这些共生微藻，从而导致珊瑚变色。减少这些微藻中ROS的产生并增强解毒过程对于防止珊瑚礁生态系统崩溃至关重要。然而，由于克隆这些微藻存在挑战，对珊瑚共生甲藻的细胞生理学和遗传学研究受到了阻碍。
本研究开发了一种克隆珊瑚共生甲藻的方法。成功克隆了几种珊瑚共生体，并对其中两种进行了进一步表征。对从旋花珊瑚属分离出的两个物种进行的实验表明，340 μmol光子/（米²·秒）的光照强度造成的损害比36°C的高温更为严重。此外，在高盐度条件下预培养可激活它们对白化胁迫的内源性耐受性。与在30 ppt盐度下培养的细胞相比，在50 ppt盐度下预处理可使处于白化胁迫下的两个物种中ROS染色细胞的百分比分别降低59%和64%。此外，与对照相比，它们在恢复期的Fv'/Fm'有显著改善。
这些发现表明，在珊瑚白化过程中，强光通过增强共生甲藻中ROS的产生比高温起着更重要的作用。研究结果还表明，珊瑚共生甲藻的基因组经历了进化过程，以发展出受基因表达调控的机制，减轻高温和强光胁迫造成的损害。了解这种基因表达调控可能有助于增强珊瑚对全球气候变化影响的恢复力。
