Beijing Vegetable Research Center, Beijing Academy of Agriculture and Forestry Sciences/Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing, 100097, China.
National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China.
Sci Rep. 2018 Sep 20;8(1):14109. doi: 10.1038/s41598-018-32472-5.
Onion (Allium cepa L.) is an important bulbous vegetable crop that possesses important properties related to health as well as extraordinary colors. Naturally white onion bulbs were used in this study to reveal the complex metabolic mechanisms that underlie phenotypic traits, especially bulb pigmentation. Six libraries (three dark-red and three white) were constructed and analyzed to elucidate differences in cyanidin (Cy) metabolism between dark-red and white onion bulbs. Libraries were screened using RNA-sequencing (RNA-seq) to reveal the differentially expressed genes (DEGs) involved in anthocyanin biosynthesis at the transcriptional level. Comparison with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database shows that a total of 27 unigenes participate in onion anthocyanin biosynthesis and 16 DEGs perform critical roles in flavonoid biosynthesis. Expression patterns of color-related flavonoid compounds associated with the onion anthocyanin biosynthesis pathway (ABP) show that flavonoid 3',5'-hydroxylase (F3'5'H) and dihydroflavonol 4-reductase (DFR) genes play crucial roles in the biosynthesis of dark-red bulbs, the expression levels of flavonol synthase (FLS) and DFR genes may act to block blue pigmentation, and the loss of Cy from white onion bulbs might explain multibranching in the synthesis of this compound. Positive variation in the F3'5'H/F3'H ratio also affects onion bulb color diversity. The transcriptome presented here provides a basis for future onion molecular breeding based on variations in the diversity of ornamental plant pigmentation.
洋葱（Allium cepa L.）是一种重要的鳞茎类蔬菜作物，具有与健康相关的重要特性以及非凡的颜色。本研究选用天然白皮洋葱鳞茎，揭示了与表型特征相关的复杂代谢机制，尤其是鳞茎色素沉着。构建并分析了六个文库（三个深紫红色和三个白色），以阐明深紫红色和白色洋葱鳞茎中花青素（Cy）代谢的差异。利用 RNA 测序（RNA-seq）筛选文库，揭示了转录水平上参与类黄酮生物合成的差异表达基因（DEGs）。与京都基因与基因组百科全书（KEGG）数据库比较表明，共有 27 个基因参与洋葱花色素苷生物合成，16 个 DEG 在类黄酮生物合成中发挥关键作用。与洋葱花色素苷生物合成途径（ABP）相关的颜色相关类黄酮化合物的表达模式表明，类黄酮 3'，5'-羟化酶（F3'5'H）和二氢黄酮醇 4-还原酶（DFR）基因在深紫红色鳞茎的生物合成中起关键作用，类黄酮合成酶（FLS）和 DFR 基因的表达水平可能阻止蓝色色素沉着，而 Cy 从白皮洋葱鳞茎中的丢失可能解释了该化合物合成中的多分支。F3'5'H/F3'H 比值的正向变化也影响洋葱鳞茎颜色的多样性。本研究提供的转录组为基于观赏植物色素多样性的洋葱分子育种提供了基础。
