中国野生拟南芥适应不同生境温度的分子机制

Plants have gradually adapted to the temperatures of habitats in the process of evolution. The populations of Arabidopsis thaliana along the Yangtze River originated from a most recent common ancestor and are located at the most southeastern edge of the global distribution range of the species. Previous studies by this applicant revealed that the sequence variation of transcription factors CBF1~3 was one of the major causes of differentiation of freezing tolerance among these populations, and that the survival rates of the populations under high-temperature were significantly correlated to the average temperature of the growing season at the habitats where they naturally grew. In this proposal, in order to address the scientific question “what is the evolutionary significance of the variations in CBF1~3 during the process of adaptation to low-temperature in these populations?”, this applicant proposes to sequence the CBF1~3 in all populations along the Yangtze River (more than 5 individuals per population will be selected), and these sequences will be classified into different haplotypes together with the samples of some representative populations from locations outside China. A molecular evolution analysis on the sequences of CBF1~3 and the transactivation activities of CBF1~3 will be examined for each haplotype. To elucidate the mechanism for differentiation of the heat-tolerance in plants, the applicant proposes to analyze the heat-treated transcriptome of some representative populations both along the Yangtze River and in other localities by RNAseq method. QTL-mapping will be adopted to identify the genetic loci responsible for significantly expressed in some populations but not in other populations. Candidate genes will be selected based on the transcriptome and QTLs, and the correlation among their sequences, functions, molecular-evolutionary characteristics, and high temperature-tolerance will be analyzed. It is hoped that a molecular mechanism of adaptation of the populations along the Yangtze River to high temperatures will be revealed.

植物在长期演化过程中逐步适应了其生境的温度。长江流域的拟南芥居群起源于一个最近的共同祖先，并处于该物种全球分布区的东南边缘。申请人前期对这些居群的耐冻能力以及高温下的生存能力进行了初步研究，发现转录因子CBF1~3的变化是这些居群耐冻能力分化的主要原因之一，这些居群在高温下的存活率与其生境的平均温度显著相关。本申请计划在前期研究的基础上采用遗传学、生化及分子生物学、分子演化分析等手段，对长江流域及全世界各生境中代表性居群的CBF1~3 DNA序列、基因选择压力、蛋白激活活性等进行研究，以揭示这些居群中CBFs在适应环境低温中的作用。通过RNA-seq等技术对代表性居群中高温响应基因表达谱进行分析，结合QTL作图等方法研究热响应差异的分子基础，用遗传学、生化及分子生物学等方法对筛选到的关键候选基因进行DNA序列、蛋白功能、基因选择压力等方面的研究，初步揭示这些居群对环境高温适应的分子机制。

拟南芥是一种在世界范围内广泛分布的短命植物，其生境的气候条件有着很大的差异。在自然选择的驱动下，植物会发生适应性演化。中国长江流域的拟南芥居群起源于一个最近的共同祖先，并处于该物种欧亚大陆分布区的东南边缘。本项目采用遗传学、生物化学、分子生物学、生物信息学、分子演化分析等手段，对中国野生拟南芥环境适应的分子机制进行了一系列深入的研究。.用CRISPR技术研究发现，冷响应途径中的三个CBF转录因子（CBF1~3）分别调控了各自的下游基因，既有特异、又有重叠的成分，它们共同行使功能，形成一个复杂的转录调控网络，在植物应答低温逆境中发挥重要作用。对长江流域拟南芥耐受低温的研究发现， CBF1~3存在多态性，其功能的差异与植株的耐冷能力以及地理分布相关，暗示了它们受到不同程度的选择压力，这样的变化对世界范围内自然居群的适应性起到了重要贡献。不同生境的野生居群可能拥有不同的机制调控其生活史，如对西藏高原拟南芥的研究发现，其种子萌发滞后，避开了低温的冬季，导致演化出了多个性状来适应新的生活史。.综上研究结果表明，植物适应新环境的过程是非常精细、复杂和多样的，对其分子机制的探索不但能进一步加深对适应性演化过程的理解，同时也可能找到更多在胁迫环境下具有适应性意义的基因。