Little is known about the factors regulating carotenoid biosynthesis in roots. In this study, we characterized DCAR_032551, the candidate gene of the Y locus responsible for the transition of root color from ancestral white to yellow during carrot (Daucus carota) domestication. We show that DCAR_032551 encodes a REPRESSOR OF PHOTOSYNTHETIC GENES (RPGE) protein, named DcRPGE1. DcRPGE1 from wild carrot (DcRPGE1W) is a repressor of carotenoid biosynthesis. Specifically, DcRPGE1W physically interacts with DcAPRR2, an ARABIDOPSIS PSEUDO-RESPONSE REGULATOR2 (APRR2)-like transcription factor. Through this interaction, DcRPGE1W suppresses DcAPRR2-mediated transcriptional activation of the key carotenogenic genes phytoene synthase 1 (DcPSY1), DcPSY2, and lycopene ε-cyclase (DcLCYE), which strongly decreases carotenoid biosynthesis. We also demonstrate that the DcRPGE1W–DcAPRR2 interaction prevents DcAPRR2 from binding to the RGATTY elements in the promoter regions of DcPSY1, DcPSY2, and DcLCYE. Additionally, we identified a mutation in the DcRPGE1 coding region of yellow and orange carrots that leads to the generation of alternatively spliced transcripts encoding truncated DcRPGE1 proteins unable to interact with DcAPRR2, thereby failing to suppress carotenoid biosynthesis. These findings provide insights into the transcriptional regulation of carotenoid biosynthesis and offer potential target genes for enhancing carotenoid accumulation in crop plants.

中文翻译：

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Y 基因座编码光合基因抑制蛋白，通过与胡萝卜中的 APRR2 相互作用来抑制类胡萝卜素生物合成

关于根中调节类胡萝卜素生物合成的因素知之甚少。在这项研究中，我们鉴定了 DCAR_032551，它是 Y 基因座的候选基因，负责胡萝卜 (Daucus carota) 驯化过程中根部颜色从祖先的白色转变为黄色。我们发现 DCAR_032551 编码光合基因阻遏物 (RPGE) 蛋白，名为 DcRPGE1。来自野胡萝卜的 DcRPGE1 (DcRPGE1W) 是类胡萝卜素生物合成的抑制剂。具体来说，DcRPGE1W 与 DcAPRR2（一种拟南芥伪响应调节器 2 (APRR2) 样转录因子）发生物理相互作用。通过这种相互作用，DcRPGE1W 抑制 DcAPRR2 介导的关键胡萝卜素基因八氢番茄红素合酶 1 (DcPSY1)、DcPSY2 和番茄红素 ε-环化酶 (DcLCYE) 的转录激活，从而强烈降低类胡萝卜素生物合成。我们还证明，DcRPGE1W-DcAPRR2 相互作用阻止 DcAPRR2 与 DcPSY1、DcPSY2 和 DcLCYE 启动子区域中的 RGATTY 元件结合。此外，我们在黄色和橙色胡萝卜的 DcRPGE1 编码区中发现了一个突变，该突变导致编码截短的 DcRPGE1 蛋白的选择性剪接转录本的生成，无法与 DcAPRR2 相互作用，从而无法抑制类胡萝卜素生物合成。这些发现提供了对类胡萝卜素生物合成转录调控的见解，并为增强作物中类胡萝卜素的积累提供了潜在的靶基因。