The carotenoid content of plants can be increased by overexpression of the regulatory protein ORANGE (OR) or a mutant variant known as the ‘golden SNP’. In the present study, a strong light-inducible promoter was used to overexpress either wild type CrOR (CrOR^WT) or a mutated CrOR (CrOR^His) containing a single histidine substitution for a conserved arginine in the microalgae Chlamydomonas reinhardtii. Overexpression of CrOR^WT and CrOR^His roughly doubled and tripled, respectively, the accumulation of several different carotenoids, including β-carotene, α-carotene, lutein and violaxanthin in C. reinhardtii and upregulated the transcript abundance of nearly all relevant carotenoid biosynthetic genes. In addition, microscopic analysis revealed that the OR transgenic cells were larger than control cells and exhibited larger chloroplasts with a disrupted morphology. Moreover, both CrOR^WT and CrOR^His cell lines showed increased tolerance to salt and paraquat stress. The levels of endogenous phytohormone abscisic acid (ABA) were also increased in CrOR^WT and CrOR^His lines, not only in normal growth conditions but also in growth medium supplemented with salt and paraquat. Together these results offer new insights regarding the role of the native OR protein in regulating carotenoid biosynthesis and the accumulation of several carotenoids in microalgae, and establish a new functional role for OR to modulate oxidative stress tolerance potentially mediated by ABA.

植物的类胡萝卜素含量可以通过调节蛋白 ORANGE (OR) 或称为“黄金 SNP”的突变变体的过度表达来增加。在本研究中，强光诱导启动子用于过表达野生型CrOR ( CrOR ^WT ) 或突变的CrOR ( CrOR ^His )，其中含有单个组氨酸替代莱茵衣藻中保守的精氨酸。CrOR ^WT和CrOR ^{His 的}过度表达分别使几种不同的类胡萝卜素（包括 β-胡萝卜素、α-胡萝卜素、叶黄素和紫黄质）的积累分别增加了一倍和三倍。C. reinhardtii并上调几乎所有相关类胡萝卜素生物合成基因的转录本丰度。此外，显微分析显示OR转基因细胞比对照细胞大，并表现出更大的叶绿体，其形态被破坏。此外，CrOR ^WT和CrOR ^His细胞系均显示出对盐和百草枯胁迫的耐受性增加。CrOR ^WT和CrOR ^His中内源性植物激素脱落酸 (ABA) 的水平也增加品系，不仅在正常生长条件下，而且在添加了盐和百草枯的生长培养基中。这些结果共同提供了关于天然 OR 蛋白在调节类胡萝卜素生物合成和微藻中几种类胡萝卜素积累中的作用的新见解，并为OR调节可能由 ABA 介导的氧化应激耐受性建立了新的功能作用。