模式硅藻在不同光照强度下对海洋酸化的转录组水平响应

The effects of ocean acidification (OA) caused by anthropogenic CO2 emissions on primary production of phytoplankton are controversial. The latest results demonstrated that the impacts of OA on the dominant phytoplankton diatoms depend on intensities of solar radiation and depth distribution. Rising CO2 levels combined with decreased light exposure in relatively deeper seawater can stimulate the growth of diatoms. However, Rising CO2 levels combined with increased light exposure negatively impacts on primary production of diatoms in oceanic surface waters while photoinhibition and photorespiration of diatoms are enhanced. This research in some extent explained the controversy of previous reports. But the molecular mechanism of this phenomenon is yet to be explored. It is known that CO2 Concentration Mechanism (CCM) has been evolved in diatoms. But the metabolic pathway of CCM is still obscure. The latest studies based on molecular and biochemical experiments suggested that this mechanism is implicated in light intensity. This project focuses on the impacts of interaction between light intensity and OA on primary production of diatoms. RNA-seq technique will be utilized to investigate the genetic responses of the model diatom species Phaeodactylum tricornutum to OA stress under different light intensities. The dynamic of involved metabolic pathways will be dissected as well based on RNA-seq data. Meanwhile, related physiological parameters of P. tricornutum under different conditions will be measured. Combined with the progresses in physiological and ecological aspects, effects of OA combined with light intensity on primary production of diatoms can be analyzed in different scales. Mesocsom experiments, carrying out in natural environment under controlled conditions, will be used as a powerful research tool in this project.

人类活动引起的海洋酸化对浮游植物初级生产力的影响存在争议。最新的结果表明：海洋酸化对硅藻这一重要浮游植物类群初级生产力的正负影响，取决于阳光辐射高低：在光强较弱的较深层海水中，CO2升高对硅藻的生长有促进作用；然而在光强较强的表层海水中，CO2升高促进了光胁迫和光呼吸，对硅藻的初级生产力产生了负影响。这一研究解释了之前研究的不一致性，但是其分子生物学机制尚不清楚。硅藻在历史进化中形成了二氧化碳浓缩机制，但是具体的代谢途径研究不是很透彻，最近的分子生物学研究表明硅藻的二氧化碳浓缩机制和光照强度密切相关。为此，本项目拟从光照强度入手，结合中型生态系统实验(Mesocosm)，利用转录组测序研究不同光照强度下海洋酸化胁迫对模式硅藻三角褐指藻（Phaeodactylum tricornutum）的影响，分析其在基因和代谢水平上的动态变化，从分子水平分析光照强度和海洋酸化对硅藻初级生产力的协同效应。

人类活动造成的海洋酸化近年来受到广泛关注。本研究以模式硅藻三角褐指藻作为研究对象，在模拟未来海洋酸化环境下培养该藻，在生理现象的基础上探索三角褐指藻应对海洋酸化的分子机制。结果显示不同株系的三角褐指藻对海洋酸化的响应有差异。分离自中国南海的三角褐指藻PtSCS在海洋酸化条件下生长和碳固定增强，β-碳酸酐酶在HC的条件下下调，这和之前的研究结果相吻合，一定程度上更进一步证实三角褐指藻在高二氧化碳条件下CCM的下调。 此外，值得注意的是亚硝酸还原酶在海洋酸化条件下表达明显增强，由此推论，二氧化碳浓缩机制（CCM）下调引起的能量节省以及氮吸收相关基因的上调，有可能是三角褐指藻在海洋酸化条件下生长和光合作用增强的原因。而分离自的三角褐指藻Pt1在海洋酸化条件下，生长速率、最大光合电子传递速率、光合效率、光合色素都未受到明显影响。然而从基因组和转录组水平分析，海洋酸化对三角褐指藻产生了较大的影响。与CCM相关的基因如编码碳酸酐酶基因、二磷酸核酮糖氧合酶/羧化酶在海洋酸化条件下出现了下调，这和之前的研究相一致。除此之外特别值得注意的是，三角褐指藻在海洋酸化条件下培养15代时，染色质结构相关蛋白基因表达水平整体下降，转座子相关基因整体上调。但是当培养到28代时，组蛋白基因的表达下调以及转座子基因的表达上调现象消失了。组蛋白对基因组结构的稳定性有重要意义，而转座子的活跃容易造成功能基因和调控系统的变异。由此推测，组蛋白和转座子的相关表观遗传学的调控存在于较短的时间尺度之内，在这时间段内基因组整体结构受到威胁，更容易产生基因突变并受到外界基因转移的影响，这对三角褐指藻在海洋酸化条件下的长期进化具有深远影响。