College of Horticulture, South China Agricultural University, Guangzhou, China.
Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China.
Physiol Plant. 2022 Sep;174(5):e13773. doi: 10.1111/ppl.13773.
Anthocyanins, vital metabolites in plants, are formed by anthocyanidins combined with various monosaccharides, including glucose, rhamnose, and arabinose. Rhamnose contributes greatly to the glycosylation of anthocyanidins. There are two kinds of rhamnose synthase (RS): rhamnose biosynthesis (RHM), and nucleotide-RS/epimerase-reductase (UER1). Nevertheless, no RS isoform was reported to be involved in anthocyanin synthesis. Here, three homologous PhRHM genes, namely PhRHM1, PhRHM2, and PhRHM3, and one PhUER1 gene from petunia were cloned and characterized. Green fluorescent protein fusion protein assays revealed that PhRHMs and PhUER1 are localized in the cytoplasm. We obtained PhRHM1 or/and PhRHM2 or PhUER1 silenced petunia plants and did not attempt to obtain PhRHM3 silenced plants since PhRHM3 mRNA was not detected in petunia organs examined. PhRHM1 and PhRHM2 (PhRHM1-2) silencing induced abnormal plant growth and decreased the contents of l-rhamnose, photosynthetic pigments and total anthocyanins, while PhUER1 silencing did not cause any visible phenotypic changes. Flavonoid metabolome analysis further revealed that PhRHM1-2 silencing reduced the contents of anthocyanins with rhamnose residue. These results revealed that PhRHMs contribute to the biosynthesis of rhamnose and that PhRHMs participate in the anthocyanin rhamnosylation in petunia, while PhUER1 does not.
花色素苷是植物中重要的代谢物，由花色苷与各种单糖结合而成，包括葡萄糖、鼠李糖和阿拉伯糖。鼠李糖对花色苷的糖基化有很大贡献。有两种鼠李糖合酶（RS）：鼠李糖生物合成（RHM）和核苷酸-RS/差向异构酶-还原酶（UER1）。然而，目前还没有报道 RS 同工酶参与花色素苷的合成。在这里，我们从矮牵牛中克隆和鉴定了三个同源的 PhRHM 基因，即 PhRHM1、PhRHM2 和 PhRHM3，以及一个 PhUER1 基因。绿色荧光蛋白融合蛋白分析表明 PhRHMs 和 PhUER1 定位于细胞质中。我们获得了沉默 PhRHM1 或/和 PhRHM2 或 PhUER1 的矮牵牛植物，并且由于在检查的矮牵牛器官中未检测到 PhRHM3 mRNA，因此未尝试获得沉默 PhRHM3 的植物。PhRHM1 和 PhRHM2（PhRHM1-2）沉默导致植物生长异常，降低了 l-鼠李糖、光合色素和总花色素苷的含量，而 PhUER1 沉默则没有引起任何可见的表型变化。类黄酮代谢组学分析进一步表明，PhRHM1-2 沉默降低了含有鼠李糖残基的花色素苷含量。这些结果表明 PhRHMs 有助于鼠李糖的生物合成，并且 PhRHMs 参与矮牵牛花色素苷的鼠李糖基化，而 PhUER1 则不参与。
