β-carotene is an efficient antioxidant and its accumulation is an oxidative response to stressors. Dunaliella salina strain GY-H13 is rich in β-carotene under environmental stresses, which was selected as material to understand the molecular mechanism underlying β-carotene biosynthesis. Seven full length cDNA sequences in β-carotene biosynthesis pathway were cloned, including geranylgeranyl pyrophosphate synthase (GGPS), phytoene synthase (PSY), phytoene desaturase (PDS), 15-cis-zeta-carotene isomerase (ZISO), zeta-carotene desaturase (ZDS), prolycopene isomerase (CRTISO), lycopene beta-cyclase (LCYb). The seven protein sequences from the strain GY-H13 showed the highest similarity with other D. salina strains. Especially, PSY, PDS and LCYb protein sequences shared 100 % identity. Phylogenetic analysis indicated all proteins from GY-H13 firstly clustered with those from other D. salina strains with a bootstrap of 100 %. Multiple alignment indicated several distinct conserved motifs such as aspartate-rich domain (ARD), dinucleotide binding domain (DBD), and carotene binding domain (CBD). These motifs are located near ligand-binding pocket, which may be required for the activity of enzyme. Expression levels of these genes and β-carotene content were measured over 24-h cycle, showing clear daily dynamics. All genes were dramatically up-regulated in the morning but the highest accumulation of β-carotene was observed at noon, suggesting a lag-effect between gene transcription and biological response. Furthermore, the accumulation of β-carotene increased under nitrogen deficiency, Cd exposure and high light and decreased under high salinity in a time-dependent manner. No gene of β-carotene biosynthesis was up-regulated by high salinity while most genes were activated by the other stresses at the beginning stage of exposure. Growth inhibition and oxidative damage were also observed under high salinity. Overall, transcription activation of β-carotene biosynthetic genes at the initial stage of stress exposure is a determinant of the increased accumulation of β-carotene in microalgae, which help their survive under harsh environments. The newly isolated D. salina strain GY-H13 would be a promising microalgae model for investigating the molecular mechanism of stress-induced β-carotene biosynthesis.

中文翻译：

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应激初期β-胡萝卜素生物合成基因的转录激活是分离的杜氏盐藻GY-H13中β-胡萝卜素积累增加的指示。

β-胡萝卜素是一种有效的抗氧化剂，其积累是对应激源的氧化反应。杜氏盐藻盐藻GY-H13在环境胁迫下富含β-胡萝卜素，被选作了解β-胡萝卜素生物合成基础分子机制的材料。克隆了β-胡萝卜素生物合成途径中的7个全长cDNA序列，包括香叶基香叶基香叶基焦磷酸合酶（GGPS），并四苯合酶（PSY），并四氢番茄红素去饱和酶（PDS），15-顺式-ζ-胡萝卜素异构酶（ZISO），ζ-胡萝卜素去饱和酶（ZDS），番茄红素异构酶（CRTISO），番茄红素β-环化酶（LCYb）。来自菌株GY-H13的七个蛋白质序列显示出与其他D. salina菌株的最高相似性。尤其是PSY，PDS和LCYb蛋白序列具有100％的同一性。系统发育分析表明，GY-H13的所有蛋白质首先与其他D. salina菌株的蛋白质聚在一起，自举率为100％。多重比对表明了几个不同的保守基序，例如富含天冬氨酸的结构域（ARD），二核苷酸结合结构域（DBD）和胡萝卜素结合结构域（CBD）。这些基序位于配体结合袋附近，这可能是酶活性所必需的。在24小时周期内测量了这些基因的表达水平和β-胡萝卜素含量，显示出清晰的每日动态。所有基因在早上都有明显的上调，​​但在中午观察到最大的β-胡萝卜素积累，表明基因转录和生物学反应之间存在滞后效应。此外，氮缺乏时β-胡萝卜素的积累增加，Cd暴露于高光下，在高盐度下呈时间依赖性降低。高盐度下没有β-胡萝卜素生物合成的基因被上调，而大多数基因在暴露初期被其他胁迫激活。在高盐度下也观察到生长抑制和氧化损伤。总体而言，在应激暴露初期，β-胡萝卜素生物合成基因的转录激活是微藻中β-胡萝卜素积累增加的决定因素，这有助于它们在恶劣环境下生存。新分离出的盐藻D. salina菌株GY-H13将是一个有前途的微藻模型，用于研究应激诱导的β-胡萝卜素生物合成的分子机制。高盐度下没有β-胡萝卜素生物合成的基因被上调，而大多数基因在暴露初期被其他胁迫激活。在高盐度下也观察到生长抑制和氧化损伤。总体而言，在应激暴露初期，β-胡萝卜素生物合成基因的转录激活是微藻中β-胡萝卜素积累增加的决定因素，这有助于它们在恶劣环境下生存。新分离出的盐藻D. salina菌株GY-H13将是一个有前途的微藻模型，用于研究应激诱导的β-胡萝卜素生物合成的分子机制。高盐度下没有β-胡萝卜素生物合成的基因被上调，而大多数基因在暴露初期被其他胁迫激活。在高盐度下也观察到生长抑制和氧化损伤。总体而言，在应激暴露初期，β-胡萝卜素生物合成基因的转录激活是微藻中β-胡萝卜素积累增加的决定因素，这有助于它们在恶劣环境下生存。新分离出的盐藻D. salina菌株GY-H13将是一个有前途的微藻模型，用于研究应激诱导的β-胡萝卜素生物合成的分子机制。应力暴露初期β-胡萝卜素生物合成基因的转录激活是微藻中β-胡萝卜素积累增加的决定因素，有助于其在恶劣环境下生存。新分离出的盐藻D. salina菌株GY-H13将是一个有前途的微藻模型，用于研究应激诱导的β-胡萝卜素生物合成的分子机制。应力暴露初期β-胡萝卜素生物合成基因的转录激活是微藻中β-胡萝卜素积累增加的决定因素，这有助于它们在恶劣环境下生存。新分离出的盐藻D. salina菌株GY-H13将是一个有前途的微藻模型，用于研究应激诱导的β-胡萝卜素生物合成的分子机制。