β酮脂酰ACP合成酶II（KASII）是催化棕榈酸（16〖DK〗∶0ACP）延伸为硬脂酸（18〖DK〗∶0ACP）的关键酶，其活性强弱决定着18碳脂肪酸含量的高低。本文以杜氏盐藻（Dunaliella salina）为试材, 分离鉴定杜氏盐藻DsKASII基因编码序列，采用生物信息学工具解析DsKASII酶蛋白的亚细胞定位、高级结构、理化性质及系统发育等特性。检测氮胁迫下的DsKASII表达量，以及藻细胞脂肪酸、叶绿素和β胡萝卜素的含量。结果表明，DsKASII编码的酶蛋白长度为476 aa，pI为6.99，含叶绿体靶向肽和较多亲水区。二级结构主要由α螺旋（22.48％），β片层（22.06％）和无规则卷曲（55.46％）组成。三级结构预测表明该蛋白整体呈紧密的心形结构, 活性酶蛋白为同源二聚体。系统发育分析表明，DsKASⅡ氨基酸序列与莱茵衣藻CrKASII同源性达99%，可能二者有着共同的进化祖先。qRTPCR揭示，与正常培养的杜氏盐藻相比，DsKASII在氮胁迫条件下的表达量明显上调，第3天时的表达量比正常培养的高4.5倍。氮胁迫下藻细胞总油脂、油酸（C18〖DK〗∶1）和类胡萝卜素含量显著提高，然而棕榈酸（C16〖DK〗∶0）和叶绿素的含量明显降低。这表明，氮胁迫诱导杜氏盐藻DsKASII基因上调表达，将更多的棕榈酸催化为硬脂酸，进而提高了单不饱和油酸的富集以及类胡萝卜素的积累。本研究为后续进一步解析杜氏盐藻氮胁迫条件下，油脂与胡萝卜素合成积累及藻细胞响应胁迫机制和优质富油藻种培育提供了科学参考。

βketoacylACP synthase II (KASII)is a key enzyme responsible for the conversion of palmitic acid (16〖DK〗∶0ACP)to stearic acid (18〖DK〗∶0ACP). KASII activity determines the level of C18 fatty acids. In this paper, Dunaliella salina was used to isolate and identify the DsKASII gene. Bioinformatics tools were used to analyze the subcellular localization, protein structure, physicochemical properties and phylogenetic characteristics of DsKASII enzyme. Detail examinations were conducted for DsKASII gene expression pattern, oil/fatty acid profiles, the contents of chlorophyll and βcarotene under nitrogen deficiency stress. The results showed that  Dunaliella salina DsKASII enzyme protein had a length of 476 aa and a theoretical isoelectric point of 6.99. The protein contained plastidtargeting peptide and many hydrophilic regions. The main secondary structures included αhelix (22.48%), βsheet (22.06%), and random coil (55.46%). The 3D structure simulation predicted that the DsKASII was compactly heartshaped structure on the whole, with a homodimer as the functional form. Phylogenetic analysis indicated that DsKASII protein has the highest homology with Chlamydomonas reinhardtii CrKASII by 99%. It is possible that the two microalgae have a common evolutionary ancestor. Quantitative RTPCR (qRCPCR)analysis revealed that the expression level of DsKASII gene was upregulated in algal cells under nitrogen deficiency stress compared with the normal culture controls. The expression level of DsKASII in the stressed cells was 4.5 times higher than that in the normal culture cells on the 3th day of cultivation. Moreover, under nitrogen stress, the total oil, oleic acid (C18〖DK〗∶1)and carotenoid content in algae cells increased significantly, whereas palmitic acid (C16〖DK〗∶0)and chlorophyll contents decreased. Taken together, the data indicated that nitrogen stress induced the upregulation of DsKASII gene in Dunaliella salina, and then DsKASII catalyzed more palmitic acid into stearic acid, eventually increasing the accumulation of monounsaturated oleic acid and carotenoids. The present study provides a scientific reference for the further analysis on the mechanism underlying accumulation of oil and carotenoids as well as algal response to the stress, benefiting the breeding of highquality oleaginous microalgae.