Abstract Astaxanthin is a highly valuable derivative of β-carotene, as well as an important raw material for pharmacy and healthy industries. Dunaliella salina is a halotolerant green alga that contains manifold nutriments and possesses a remarkable ability to adapt environment. The alga is also able to effectively accumulate β-carotene up to 10% of its dry weight. However, D. salina is lack of the enzymes for astaxanthin synthesis so that the accumulated β-carotene cannot be converted to astaxanthin in the alga. The designed experiment was that the exogenous key enzyme genes for astaxanthin synthesis, β-carotene ketolase and β-carotene hydroxylase cloned from Haematococcus pluvialis (Chlorophyceae), were co-transformed into D. salina by bombardment deliver system. The observation of laser scanning confocal microscope and analysis of PCR amplification confirmed the efficient expression of the transformed genes. Compared with the wild type strain, the transformants showed stronger high irradiation adaptability with higher cell survival rate, light saturation point, maximum relative electron transport rate and lower ROS level. The results of biochemical analysis indicated that the activities of antioxidant enzymes showed no significant difference between the two groups. At the transcriptional level, four carotenogenic genes (PSY, PDS, ZDS, LCYB) expressed 2~4 fold higher in the transformants than in the wild type. The tested transformants treated under high irradiation intensity were able to synthesize astaxanthin and the amount of astaxanthin was 5.56 μg/g dry weight measured by HPLC. This study may provide fundamental data for metabolic engineering to synthesize astaxanthin in D. salina.

中文翻译：

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转基因盐生杜氏藻（叶绿科）中虾青素的生物合成增强了对高辐射胁迫的耐受性

摘要 虾青素是一种价值很高的β-胡萝卜素衍生物，是制药和健康产业的重要原料。盐生杜氏藻是一种耐盐绿藻，含有多种营养物质，具有显着的环境适应能力。藻类还能够有效地积累高达其干重 10% 的 β-胡萝卜素。然而，D. salina 缺乏合成虾青素的酶，因此积累的β-胡萝卜素不能在藻类中转化为虾青素。设计的实验是将雨生红球藻(叶绿科)克隆的外源虾青素合成关键酶基因β-胡萝卜素酮醇酶和β-胡萝卜素羟化酶通过轰击传递系统共转化到D. salina中。激光扫描共聚焦显微镜观察和PCR扩增分析证实了转化基因的有效表达。与野生型菌株相比，转化体表现出更强的高辐照适应性，具有更高的细胞存活率、光饱和点、最大相对电子传递率和更低的ROS水平。生化分析结果表明，两组抗氧化酶活性无显着差异。在转录水平上，转化体中四种胡萝卜素基因（PSY、PDS、ZDS、LCYB）的表达量是野生型的 2~4 倍。受试转化体在高辐照强度下能够合成虾青素，HPLC测得虾青素含量为5.56 μg/g干重。