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.

中文翻译：

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萝卜主根中花青素的差异积累：RsMYB1基因结构的重要性。

RsMYB1a是重要的MYB，而RsbHLH4是调节萝卜花青素生物合成的重要伙伴。根据花青素是否在主根的皮和肉中积累，萝卜有四种颜色类型。红萝卜在皮和肉中都积累了大量的花青素。众所周知，MYB-bHLH-WD40 转录因子复合物调节植物中花青素的生物合成。在这里，四个候选MYB和bHLH基因，RsMYB1a，RsMYB1b，RsbHLH2和RsbHLH4，是从红萝卜'红心1'中分离出来的。RsbHLH4和两个结构基因RsANS和RsUFGT的表达与花青素含量呈显着正相关。RsMYB1a 的表达也与花青素的积累高度相关，尤其是剔除‘红心1-1’的白肉样品时。RsMYB1a在萝卜子叶和叶片中的瞬时表达诱导花青素积累，与RsbHLH4联合表达时具有更强的促进作用。这些结果表明RsMYB1a是至关重要的MYB，而RsbHLH4是调节萝卜花青素生物合成的重要伙伴。低或检测不到的 RsbHLH4 表达与'红心 1-1' 和'沙冠 1' 的白色果肉中缺乏花青素积累相似。测定表明，RsMYB1a 与 RsbHLH4 相互作用并激活 RsbHLH4 的表达。值得注意的是，所有深红色萝卜品种都有较长的 RsMYB1a 基因组 DNA 序列，而非红色品种中存在较短且无功能的 RsMYB1a。