Department of Biology, Hopkins Marine Station, Stanford University, 120 Ocean View Boulevard, Pacific Grove, CA 93950, USA.
Sci Adv. 2017 Mar 8;3(3):e1601298. doi: 10.1126/sciadv.1601298. eCollection 2017 Mar.
For reef-building corals, extreme stress exposure can result in loss of endosymbionts, leaving colonies bleached. However, corals in some habitats are commonly exposed to natural cycles of sub-bleaching stress, often leading to higher stress tolerance. We monitored transcription in the tabletop coral daily for 17 days over a strong tidal cycle that included extreme temperature spikes, and show that increases in temperature above 30.5°C triggered a strong transcriptional response. The transcriptomic time series data allowed us to identify a set of genes with coordinated expression that were activated only on days with strong tides, high temperature, and large diel pH and oxygen changes. The responsive genes are enriched for gene products essential to the unfolded protein response, an ancient cellular response to endoplasmic reticulum stress. After the temporary heat pulses passed, expression of these genes immediately decreased, suggesting that homeostasis was restored to the endoplasmic reticulum. In a laboratory temperature stress experiment, we found that the expression of these environmentally responsive genes increased as corals bleached, showing that the unfolded protein response becomes more intense during more severe stress. Our results point to the unfolded protein response as a first line of defense that acroporid corals use when coping with environmental stress on the reef, thus enhancing our understanding of coral stress physiology during a time of major concern for reefs.
对于造礁珊瑚来说，极端的压力暴露会导致共生体的丧失，使珊瑚白化。然而，一些栖息地的珊瑚通常会受到亚白化压力的自然周期的影响，这通常会导致更高的压力耐受性。我们在一个强烈的潮汐周期内，每天监测桌面珊瑚的转录水平长达 17 天，该周期包括极端的温度峰值，并表明温度升高超过 30.5°C 会引发强烈的转录反应。转录组时间序列数据使我们能够识别一组具有协调表达的基因，这些基因仅在强潮汐、高温以及大昼夜 pH 和氧气变化的日子里被激活。这些响应基因富集了对未折叠蛋白反应至关重要的基因产物，未折叠蛋白反应是一种古老的细胞对内质网应激的反应。在临时热脉冲过去后，这些基因的表达立即下降，表明内质网的稳态得到恢复。在实验室温度应激实验中，我们发现这些对环境有响应的基因的表达随着珊瑚白化而增加，表明在更严重的应激下，未折叠蛋白反应变得更加剧烈。我们的研究结果表明，未折叠蛋白反应是 acroporid 珊瑚在应对珊瑚礁上的环境压力时使用的第一道防线，从而增强了我们对珊瑚在主要关注珊瑚礁时期的应激生理学的理解。
