State Key Laboratory of Corp Biology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops in Huang-Huai Region, Ministry of Agriculture, College of Horticultural Science and Engineering, Shandong Agricultural University, Tai'an, Shandong, China.
International Institute for Translational Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, China.
J Exp Bot. 2019 Jan 1;70(1):69-84. doi: 10.1093/jxb/ery336.
Spine colour is an important fruit quality trait that influences the commercial value of cucumber (Cucumis sativus). However, little is known about the metabolites and the regulatory mechanisms of their biosynthesis in black spine varieties. In this study, we determined that the pigments of black spines are flavonoids, including flavonols and proanthocyanidins (PAs). We identified CsMYB60 as the best candidate for the previously identified B (Black spine) locus. Expression levels of CsMYB60 and the key genes involved in flavonoid biosynthesis were higher in black-spine inbred lines than that in white-spine lines at different developmental stages. The insertion of a Mutator-like element (CsMULE) in the second intron of CsMYB60 decreased its expression in a white-spine line. Transient overexpression assays indicated that CsMYB60 is a key regulatory gene and Cs4CL is a key structural gene in the pigmentation of black spines. In addition, the DNA methylation level in the CsMYB60 promoter was much lower in the black-spine line compared with white-spine line. The CsMULE insert may decrease the expression level of CsMYB60, causing hindered synthesis of flavonols and PAs in cucumber fruit spines.
果皮颜色是影响黄瓜（Cucumis sativus）商品价值的一个重要果实品质性状。然而，对于黑刺品种中代谢物及其生物合成的调控机制知之甚少。在本研究中，我们确定黑刺的色素为类黄酮，包括黄酮醇和原花青素（PAs）。我们鉴定出 CsMYB60 是先前鉴定的 B（黑刺）基因座的最佳候选基因。在不同发育阶段，黑刺自交系中 CsMYB60 及其参与类黄酮生物合成的关键基因的表达水平均高于白刺系。CsMYB60 第二内含子中的一个 Mutator-like 元件（CsMULE）的插入降低了白刺系中 CsMYB60 的表达。瞬时过表达试验表明，CsMYB60 是黑刺色素形成的关键调控基因，Cs4CL 是关键结构基因。此外，与白刺系相比，黑刺系中 CsMYB60 启动子的 DNA 甲基化水平要低得多。CsMULE 插入可能降低 CsMYB60 的表达水平，导致黄瓜果实刺中类黄酮和 PAs 的合成受阻。
