目的 从罗马洋甘菊Chamaemelum nobile中克隆萜类化合物合成关键酶吉马烯A合成酶（germacrene A synthase，GAS）cDNA全长，并对其进行生物信息学和组织表达分析。方法 基于前期对罗马洋甘菊转录组测序结果，设计特异性引物，利用反转录聚合酶链式反应（RT-PCR）扩增得到GAS的cDNA全长，利用生物信息学手段对其核苷酸和编码的氨基酸序列进行分析，并预测其编码的蛋白质的理化性质和功能。通过实时定量PCR技术（qRT-PCR）检测罗马洋甘菊GAS基因（CnGAS）在罗马洋甘菊不同组织的表达水平。结果 扩增得到的罗马洋甘菊吉马烯A合成酶基因的cDNA全长为1 785 bp，命名为CnGAS（GenBank登录号为KU589283），包含1个1 683 bp的开放阅读框（ORF），编码561个氨基酸，预测的相对分子质量和等电点分别为6 470和5.21。CnGAS基因编码的氨基酸序列与其他植物的GAS蛋白高度同源，且含有DDxxD保守序列。系统进化树表明CnGAS基因与菊科植物的GAS基因的亲缘关系最近。qRT-PCR结果显示CnGAS基因在罗马洋甘菊各组织中均有表达，且花中表达量最高。结论 从罗马洋甘菊中克隆得到CnGAS基因，分析了该基因在不同组织中的表达水平，为罗马洋甘菊萜类化合物的生物合成代谢途径的研究奠定了基础。

Objective Chamaemelum nobile is renowned for its production of essential oils, in which major components are sesquiterpenoids. Germacrene A synthase (GAS) is one of core enzymes involved in sesquiterpenoids. The present study aims to clone the full-length cDNA of GAS gene from C. nobile (CnGAS), and characterize and analyze tissue expression pattern of GAS gene. Methods The specific primers were designed based on the results of previous transcriptome sequencing and the full-length cDNA of CnGAS was cloned by RT-PCR. The nucleotide sequence and its encoding amino-acid sequence were analyzed by bioinformatics method, and the physicochemical property and function of the encoding protein were predicted. The expression levels of the gene in different organs of C.nobile were determined by qRT-PCR technology. Results The full-length cDNA of GAS gene, designated as CnGAS, was 1 785 bp (GenBank accession number:KU589283) and contained a 1 683 bp open reading frame (ORF), which encoded a 561 amino-acid protein. The theoretical molecular weight and PI of the deduced CnGAS protein were 6 470 and 5.21, respectively. The encoding amino-acid sequence of CnGAS showed high similarity to GAS proteins in other plants, which contained conserved DDxxD motif. Phylogenetic tree analysis revealed that CnGAS had closer genetic relationship with GASs from Asteracae plants. The result of qRT-PCR showed that CnGAS gene was expressed in different organs of C.nobile, and highly expressed in the flower. Conclusion The CnGAS gene is isolated from C.nobile and the expression levels of this gene in different organs are analyzed, which will lay a foundation for further study of sesquiterpene biosynthesis pathway in C.nobile.

国家自然科学基金资助项目（31400603）；大学生创新创业训练计划项目（201207014）