Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences; Key Laboratory of Biology and Genetic Improvement of Horticultural Crops, Ministry of Agriculture, Beijing, PR China.
Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou, 310021, PR China.
Plant Physiol Biochem. 2019 Jun;139:528-539. doi: 10.1016/j.plaphy.2019.04.006. Epub 2019 Apr 11.
The color of radish (Raphanus sativus) taproot skin is an important visual quality. 'Xinlimei' radish is a red-fleshed cultivar with skin that changes color from red to white and finally to green at the mature stage, and appearance quality is strongly affected if the red color does not fade completely on a single taproot or simultaneously among different taproots. In the present study, anthocyanin and chlorophyll contents and the transcriptome of radish taproot skin at three distinct coloration stages were analyzed to explore the mechanism of color changes. The results showed that decreased anthocyanin and increased chlorophyll contents correlated with the color-fading process. Kyoto Encyclopedia of Genes and Genomes enrichment analysis of differentially expressed genes indicated that anthocyanin and chlorophyll metabolism pathways play important roles in color changes. In red color-fading process, the expression levels of anthocyanin biosynthetic genes (except PAL and C4H), a transport gene (RsTT19), and two anthocyanin biosynthesis transcription factors (TFs), RsMYB1 and RsTT8, were significantly downregulated, whereas peroxidase-encoding genes were significantly upregulated. In the skin-greening process, expression of most chlorophyll biosynthetic genes and two TFs (RsGLK1 and RsGLK2) that likely positively regulate chlorophyll biosynthesis was significantly upregulated. Thus, changes in the expression of these genes may be responsible for the color changes that occur in 'Xinlimei' taproot skin. This is the first report on the roles of chlorophyll metabolism genes and their dynamic relationship with anthocyanin metabolism genes in radish. The findings provide valuable information and theoretical guidelines for improving the appearance quality of 'Xinlimei' radish taproots.
萝卜（Raphanus sativus）主根皮色是重要的外观品质。‘心美’萝卜是一种红心品种，成熟时皮色由红变白再变绿，如果单个主根或不同主根之间红色不能完全褪去，外观品质会受到很大影响。本研究分析了三个不同着色阶段的萝卜主根皮的花青苷和叶绿素含量及转录组，以探讨颜色变化的机制。结果表明，花青苷含量降低和叶绿素含量增加与褪色过程相关。差异表达基因的京都基因与基因组百科全书富集分析表明，花青苷和叶绿素代谢途径在颜色变化中起重要作用。在红色褪色过程中，除 PAL 和 C4H 外，花青苷生物合成基因（RsTT19）和两个花青苷生物合成转录因子（RsMYB1 和 RsTT8）的表达水平显著下调，而过氧化物酶编码基因显著上调。在皮绿化过程中，大多数叶绿素生物合成基因和两个可能正向调控叶绿素生物合成的 TFs（RsGLK1 和 RsGLK2）的表达显著上调。因此，这些基因表达的变化可能是‘心美’萝卜主根皮颜色变化的原因。这是首次报道萝卜中叶绿素代谢基因及其与花青苷代谢基因的动态关系。研究结果为提高‘心美’萝卜的外观品质提供了有价值的信息和理论指导。
