In the present study, we tested the hypothesis that high salinity acclimatization can mitigate cadmium (Cd) toxicity in the microalga Dunaliella salina. To this end, microalgal cells were subjected to high salinity (60 g/L) for 12 weeks until the growth rate remained stable between generations and were then exposed to 2.5 mg/L of Cd for 4 days. Acute Cd toxicity impaired cell growth by increasing Cd bioaccumulation and lipid peroxidation, which reduced cellular pigment, total protein, and glutathione content. It also significantly weakened photosynthetic efficiency and total antioxidant capacity. However, acclimatization to high salinity alleviated these negative effects under Cd stress. To understand the potential mechanisms behind this phenomenon, 12 cDNA libraries from control, Cd-exposed (Cd), high salinity-acclimated (Salinity), and high salinity-acclimated with Cd exposure (Salinity + Cd) cells were derived using RNA sequencing. A total of 2019, 1799, 2150 and 1256 differentially expressed genes (DEGs) were identified from sample groups Salinity / Control, Cd / Control, Salinity + Cd / Control, and Salinity + Cd / Cd, respectively. Some of these DEGs were significantly enriched in ribosome, photosynthesis, stress defense, and photosynthesis-antenna proteins. Among these genes, 82 ribosomal genes were up-regulated in Salinity / Control (corrected P = 3.8 × 10-28), while 81 were down-regulated in Cd / Control (corrected P = 1.1 × 10-24). Moreover, high salinity acclimatization up-regulated 8 photosynthesis genes and 18 stress defense genes compared with the control. Additionally, 3 photosynthesis genes, 11 stress defense genes and 11 genes encoding light harvesting proteins were up-regulated by high salinity acclimatization under Cd exposure. Overall, high salinity acclimatization mitigated Cd toxicity, possibly by up-regulating the transcription of photosynthesis, stress defense, and ribosomal genes. These results provide new insights on cross-tolerance in microalgae.

中文翻译：

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高盐度驯化减轻了杜氏盐藻中的镉毒性：转录组学和生理学证据。

在本研究中，我们测试了高盐度驯化可以减轻微藻杜氏盐藻中镉（Cd）毒性的假设。为此，对微藻细胞进行高盐度（60 g / L）处理12周，直至各代之间的生长速率保持稳定，然后将其暴露于2.5 mg / L Cd中4天。急性镉毒性通过增加镉的生物蓄积和脂质过氧化作用来损害细胞生长，从而减少细胞色素，总蛋白和谷胱甘肽的含量。它还显着削弱了光合作用效率和总抗氧化能力。然而，适应高盐度减轻了镉胁迫下的这些负面影响。为了了解这种现象背后的潜在机制，我们从对照，镉暴露（Cd），高盐度适应（盐度），使用RNA测序得出Cd暴露（盐度+ Cd）高盐度适应的细胞。分别从盐度/对照，Cd /对照，盐度+ Cd /对照和盐度+ Cd / Cd样品组中鉴定出总共2019、1799、2150和1256个差异表达基因（DEG）。这些DEG中的一些显着富含核糖体，光合作用，胁迫防御和光合作用-天线蛋白。在这些基因中，盐度/对照中有82个核糖体基因上调（校正后的P = 3.8×10-28），而镉/对照中有81个核糖体基因下调（校正后的P = 1.1×10-24）。此外，与对照相比，高盐度驯化可上调8个光合作用基因和18个逆境防御基因。此外，还有3个光合作用基因 在镉暴露下，高盐度驯化使11个胁迫防御基因和11个编码采光蛋白的基因上调。总体而言，高盐度驯化可以减轻Cd毒性，这可能是通过上调光合作用，胁迫防御和核糖体基因的转录来实现的。这些结果为微藻的交叉耐受提供了新的见解。