Shearer Tl, Rasher Db, Snell Tw, Hay Me
Georgia Institute of Technology, School of Biology, 310 Ferst Drive, Atlanta, GA 30332.
Coral Reefs. 2012 Dec;31(4):1177-1192. doi: 10.1007/s00338-012-0943-7.
Contact with macroalgae often causes coral mortality, but the roles of abrasion versus shading versus allelopathy in these interactions are rarely clear and effects on gene expression are unknown. Identification of gene expression changes within corals in response to contact with macroalgae can provide insight into the mode of action of allelochemicals, as well as reveal transcriptional strategies of the coral that mitigate damage from this competitive interaction, enabling the coral to survive. Gene expression responses of the coral after long-term (20 d) direct contact with macroalgae (, and ) and short-term (1 h and 24 h) exposure to thalli and their hydrophobic extract were assessed. After 20 d of exposure, thalli elicited no significant change in visual bleaching or zooxanthellae PSII quantum yield within nubbins, but stimulated the greatest alteration in gene expression of all treatments. and caused significant visual bleaching of coral nubbins and reduced the PSII quantum yield of associated zooxanthellae after 20 d, but elicited fewer changes in gene expression relative to at day 20. To evaluate initial molecular processes leading to reduction of zooxanthella PSII quantum yield, visual bleaching, and coral death, short-term exposures to thalli and hydrophobic extracts were conducted; these interactions revealed protein degradation and significant changes in catalytic and metabolic activity within 24 h of contact. These molecular responses are consistent with the hypothesis that allelopathic interactions lead to alteration of signal transduction and an imbalance between reactive oxidant species production and antioxidant capabilities within the coral holobiont. This oxidative imbalance results in rapid protein degradation and eventually to apoptosis and/or necrosis when compensatory transcriptional action by the coral holobiont insufficiently mitigates damage by the allelochemicals of .
与大型藻类接触常常导致珊瑚死亡，但在这些相互作用中，磨损、遮光和化感作用的角色很少清晰明确，且对基因表达的影响尚不清楚。识别珊瑚在与大型藻类接触时基因表达的变化，能够深入了解化感物质的作用模式，还能揭示珊瑚减轻这种竞争性相互作用所造成损害的转录策略，从而使珊瑚得以存活。评估了珊瑚在与大型藻类长期（20天）直接接触（、和）以及短期（1小时和24小时）暴露于藻体及其疏水提取物后的基因表达反应。暴露20天后，藻体在珊瑚断枝内未引起明显的白化或虫黄藻PSII量子产率变化，但在所有处理中刺激了最大程度的基因表达改变。和在20天后导致珊瑚断枝明显白化，并降低了相关虫黄藻的PSII量子产率，但相对于20天时的，其引起的基因表达变化较少。为了评估导致虫黄藻PSII量子产率降低、白化和珊瑚死亡的初始分子过程，进行了对藻体和疏水提取物的短期暴露；这些相互作用表明在接触24小时内发生了蛋白质降解以及催化和代谢活性的显著变化。这些分子反应与化感相互作用导致信号转导改变以及珊瑚共生体中活性氧物质产生与抗氧化能力之间失衡的假设一致。这种氧化失衡导致蛋白质快速降解，当珊瑚共生体的补偿性转录作用不足以减轻的化感物质造成的损害时，最终导致细胞凋亡和/或坏死。
