北极适冷小球藻广温适应的生理生态特征及其分子调控机制

Psychrotrophic algae, which adapt to the extremely cold and seasonal high temperature conditions, develop a distinct eurythermal adaptive mechanism from obligate psychrophilic algae. In our previous work, Chlorella sp. Lw2006/68, a psychrotrophic strain isolated from the Arctic region, was found to be able to grow well in a temperature region from 3℃ to 27℃, showing a better tolerance to thermal stress than the obligate psychrophilic algae. Under cold or thermal stress, the psychrotrophic Chlorella sp. Lw2006/68 showed significantly different responses in photosynthesis and energy metabolisms, comparing with currently reported psychrophilic algae. However, the detailed physiological and molecular mechanisms remain unrevealed. In this study, to understand the eurythermal adaptive mechanisms of the psychrotrophic Chlorella sp. Lw2006/68, the ecophysiological responses of photosynthesis and energy metabolisms to cold/thermal stress will be firstly studied. The transcriptome technology (RNA-Seq) will be employed to screen differentially expressed genes involved in protective and regulated pathways. Then the full-length cDNA of 4-5 differentially expressed genes should be cloned by RACE. Further, their expression patterns under cold/thermal stress will be studied by qRT-PCR to preliminarily clarify the molecular mechanisms underlying eurythermal adaptation. The results of this research may provide a theoretical data for understanding the unique adaptive mechanisms of polar algae to chilling and heat, and offer new insights into exploring unique stress-tolerant gene resources from polar microalgae. In addition, this study will provide theoretical support for development and utilization of psychrotrophic algae resources which could be well-grown in the cold winter.

适冷微藻能适应极地严寒和季节性的高温环境，形成了与专性嗜寒藻不同的特殊广温适应机制。我们的前期工作发现，一株从北极冰川融水中分离的适冷小球藻（Chlorella sp. Lw2006/68）在3-27℃范围内均表现出良好的生长状态，比专性嗜寒藻更耐受高温胁迫。该小球藻对低/高温胁迫的响应特征与嗜寒藻存在显著差异，但具体生理调节和分子调控机制尚不明确。本课题将在低/高温胁迫下，研究该小球藻光合作用和能量代谢的运行规律，揭示其在温度胁迫下维持基本生命活动的机理；同时采用RNA-Seq技术筛选与之适应低/高温胁迫相关的保护和调控基因，克隆鉴定4-5个关键差异基因，并分析其时相表达特征，阐明适冷小球藻特殊广温适应机制的分子调控机理。研究结果将为解析极地微藻的特殊温度适应机理提供数据资料，为发掘极地微藻中特殊的抗逆基因资源提供新的思路，也为开发适合冬季养殖的适冷藻种资源和培养技术奠定基础。

适冷微藻能适应极地严寒和季节性的高温环境，形成了与专性嗜寒藻不同的特殊广温适应机制。为阐明北极适冷小球藻（Chlorella-Arc）广温适应性的具体生理调节和分子调控机制，首先采用RNA-seq分别对不同温度（15 ℃、3 ℃、24 ℃）处理下的Chlorella-Arc进行转录组测序，鉴定了与低/高温胁迫应答相关的差异表达基因。与中温对照相比，高温处理上调/下调表达基因分别为3447/1164个，低温时上调/下调表达基因分别为1351/3109个。重点探讨了光合作用、多糖合成、脂质代谢等途径在适应高/低温过程中的应答机制，并用qRT-PCR验证关键差异基因的时序表达特征。为了探讨光合作用的运行规律及其保护调节机制，测定了PSI、PSII的光合荧光参数变化，结合转录组分析结果，发现低温下捕光复合体LHC相关基因下调表达，PSI、PSII反应中心蛋白相关基因上调表达，表明Chlorella-Arc可能通过减少光能捕获来减轻光抑制，并提高光能从天线色素传递到反应中心的效率维持较高的光化学活性；低温下叶黄素循环的关键基因lut5，lut1和zep基因表达上调，表明叶黄素循环介导的热耗散（NPQ）在低温下发挥了光保护作用。高温胁迫下，涉及多糖合成、糖异生的关键基因上调表达，而低温下一些调节碳分配和脂质合成的基因表达上调，结合生理生化指标含量变化，推测Chlorella-Arc在不同温度下通过调节碳流分配合成不同的储能物质，来适应温度变化。发现北极小球藻在抗高温胁迫过程中合成大量多糖，为了进一步分析多糖的作用，同时挖掘北极小球藻的应用价值，采用热水提取法获得了北极小球藻的粗多糖，优化提取工艺，进行体外抗氧化活性分析，发现该粗多糖具有较强的抗氧化活性。通过成分分析检测到该粗多糖含有硫酸基，具有生物活性。研究为解析极地微藻的特殊温度适应机理提供数据资料，并为开发极地微藻特殊活性物质资源提供技术支持。项目投入直接经费20万元，支出18.5532万元，节余1.4468万元，各项支出基本与预算相符。发表论文4篇，其中SCI论文3篇,接受1篇中文综述。培养博士研究生2名，硕士研究生2名。