School of Advanced Agriculture and Bioengineering, Yangtze Normal University, Chongqing, 408100, People's Republic of China.
College of Horticulture, South China Agricultural University, Guangzhou, 510642, People's Republic of China.
Plant Cell Rep. 2020 Feb;39(2):217-226. doi: 10.1007/s00299-019-02485-z. Epub 2019 Nov 14.
RsMYB1a was the crucial MYB, and RsbHLH4 is the essential partner in regulating the anthocyanin biosynthesis in radish. There are four color types of radish according to whether or not the anthocyanin accumulates in the skin and flesh of taproot. Red radishes accumulate a substantial amount of anthocyanins in both the skin and flesh. It is well known that the MYB-bHLH-WD40 transcription factor(s) complex regulates the biosynthesis of anthocyanin in plants. Here in, four candidate MYB and bHLH genes, RsMYB1a, RsMYB1b, RsbHLH2 and RsbHLH4, were isolated from red radish 'Hongxin 1'. The expression of RsbHLH4 and the two structural genes RsANS and RsUFGT was significantly positively correlated with anthocyanin contents. The expression of RsMYB1a was also highly correlated with anthocyanin accumulation, particularly when the white flesh sample of 'Hongxin 1-1' was excluded. The transient expression of RsMYB1a in the radish cotyledon and leaf induced anthocyanin accumulation with even stronger promoting role when expression in combination with RsbHLH4. These results suggested that RsMYB1a was the crucial MYB, and that RsbHLH4 is an essential partner in regulating the biosynthesis of anthocyanins in radish. The low or undetectable RsbHLH4 expression paralleled the lack of anthocyanin accumulation in the white flesh of 'Hongxin 1-1' and 'Shaguan 1'. Assays demonstrated that RsMYB1a interacted with RsbHLH4 and activated the expression of RsbHLH4. Notably, all the dark red radish cultivars have a longer RsMYB1a genomic DNA sequence, while the short and nonfunctional RsMYB1a is present in non-red cultivars. The length of the first intron and the presence of an early stop codon of RsMYB1 might underlie the differential anthocyanin accumulation in the radish taproot.
RsMYB1a 是关键的 MYB，而 RsbHLH4 是调节萝卜中花色苷生物合成的必需伙伴。根据是否在肉质根的表皮和肉质中积累花色苷，萝卜有四种颜色类型。红萝卜在表皮和肉质中都积累了大量的花色苷。众所周知，MYB-bHLH-WD40 转录因子（s）复合物调节植物花色苷的生物合成。在这里，从红萝卜“红心 1 号”中分离出四个候选 MYB 和 bHLH 基因，RsMYB1a、RsMYB1b、RsbHLH2 和 RsbHLH4。RsbHLH4 的表达以及两个结构基因 RsANS 和 RsUFGT 与花色苷含量呈显著正相关。RsMYB1a 的表达也与花色苷积累高度相关，特别是当排除“红心 1-1”的白皮样本时。RsMYB1a 在萝卜子叶和叶片中的瞬时表达诱导花色苷积累，与 RsbHLH4 表达组合时具有更强的促进作用。这些结果表明 RsMYB1a 是关键的 MYB，而 RsbHLH4 是调节萝卜花色苷生物合成的必需伙伴。“红心 1-1”和“沙关 1”白皮中花色苷积累缺乏，相应地 RsbHLH4 表达水平低或检测不到。试验表明 RsMYB1a 与 RsbHLH4 相互作用并激活 RsbHLH4 的表达。值得注意的是，所有深色红萝卜品种都具有更长的 RsMYB1a 基因组 DNA 序列，而在非红色品种中存在短的和无功能的 RsMYB1a。RsMYB1a 的第一内含子长度和提前终止密码子的存在可能是萝卜肉质根花色苷积累差异的基础。
