Key Laboratory of Horticultural Plant Biology, Ministry of Education, Key Laboratory of Horticultural Crop Biology and Genetic improvement (Central Region), MOA, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, China.
Genome Center and Department of Plant Sciences, University of California, Davis, CA, USA.
Plant Biotechnol J. 2020 Feb;18(2):479-490. doi: 10.1111/pbi.13213. Epub 2019 Aug 8.
Anthocyanins protect plants from biotic and abiotic stressors and provide great health benefits to consumers. In this study, we cloned four genes (Red Lettuce Leaves 1 to 4: RLL1 to RLL4) that contribute to colour variations in lettuce. The RLL1 gene encodes a bHLH transcription factor, and a 5-bp deletion in some cultivars abolishes its function to activate the anthocyanin biosynthesis pathway. The RLL2 gene encodes an R2R3-MYB transcription factor, which was derived from a duplication followed by mutations in its promoter region. The RLL3 gene encodes an R2-MYB transcription factor, which down-regulates anthocyanin biosynthesis through competing with RLL2 for interaction with RLL1; a mis-sense mutation compromises the capacity of RLL3 to bind RLL1. The RLL4 gene encodes a WD-40 transcription factor, homologous to the RUP genes suppressing the UV-B signal transduction pathway in Arabidopsis; a mis-sense mutation in rll4 attenuates its suppressing function, leading to a high concentration of anthocyanins. Sequence analysis of the RLL1-RLL4 genes from wild and cultivated lettuce showed that their function-changing mutations occurred after domestication. The mutations in rll1 disrupt anthocyanin biosynthesis, while the mutations in RLL2, rll3 and rll4 activate anthocyanin biosynthesis, showing disruptive selection for leaf colour during domestication of lettuce. The characterization of multiple polymorphic genes in this study provides the necessary molecular resources for the rational breeding of lettuce cultivars with distinct levels of red pigments and green cultivars with high levels of health-promoting flavonoids.
花色素苷可以保护植物免受生物和非生物胁迫，并为消费者提供巨大的健康益处。在这项研究中，我们克隆了四个与生菜颜色变化有关的基因（Red Lettuce Leaves 1 到 4：RLL1 到 RLL4）。RLL1 基因编码一个 bHLH 转录因子，某些品种中的 5 个碱基对缺失会使其丧失激活花色素苷生物合成途径的功能。RLL2 基因编码一个 R2R3-MYB 转录因子，它是由其启动子区域的重复和突变衍生而来。RLL3 基因编码一个 R2-MYB 转录因子，它通过与 RLL1 竞争相互作用来下调花色素苷生物合成；一个错义突变削弱了 RLL3 与 RLL1 结合的能力。RLL4 基因编码一个 WD-40 转录因子，与拟南芥中抑制 UV-B 信号转导途径的 RUP 基因同源；rll4 的错义突变削弱了其抑制功能，导致花色素苷浓度升高。对野生和栽培生菜的 RLL1-RLL4 基因进行序列分析表明，它们的功能改变突变发生在驯化之后。rll1 的突变破坏了花色素苷的生物合成，而 RLL2、rll3 和 rll4 的突变则激活了花色素苷的生物合成，表明在生菜驯化过程中对叶片颜色进行了破坏性选择。本研究中多个多态性基因的特征为具有不同水平红色素的生菜品种和具有高含量促进健康的类黄酮的绿色品种的合理选育提供了必要的分子资源。
