Xibei tree peony is a distinctive cultivar group that features the red-purple blotches in petals. Interestingly, the pigmentation of blotches and non-blotches is largely independent of one another. The underlying molecular mechanism had attracted lots of attention from investigators, but was still uncertain. Our present work demonstrated the factors that closely related to the blotch formation of Paeonia rockii ‘Shu Sheng Peng Mo’. The non-blotch pigmentation is prevented by the silence of anthocyanin structural genes, among which PrF3H, PrDFR, and PrANS are the three major genes. We characterized two R2R3-MYBs as the key transcription factors that control the anthocyanin early and late biosynthetic pathways, respectively. PrMYBa1, which belongs to MYB SG7 (subgroup 7) was found to activates the EBG (early biosynthetic gene) PrF3H by interacting with SG5 member PrMYBa2 to form a ‘MM’ complex. The SG6 member PrMYBa3 interacts with two SG5 (IIIf) bHLHs to synergistically activate the LBGs (late biosynthetic genes) PrDFR and PrANS, which is essential for anthocyanin accumulation in blotch of petals. The comparison of methylation levels of PrANS and PrF3H promoters between blotch and non-blotch indicated a correlation between hypermethylation and gene silencing. The methylation dynamics of PrANS promoter during flower development revealed a potential demethylating reaction in the early stage, and this reaction may have contributed to the particular expression of PrANS solely in blotch area. We suggest that the cooperation of transcriptional activation and DNA methylation of structural gene promoters may be strongly correlated with the formation of petal blotch.

中文翻译：

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DNA甲基化与MYB和bHLH转录因子对花青素生物合成的正调控相结合，有助于西贝牡丹花瓣斑块的形成

西贝牡丹是一个独特的品种群，其花瓣上有红紫色斑点。有趣的是，斑点和非斑点的色素沉着在很大程度上是彼此独立的。潜在的分子机制引起了研究人员的广泛关注，但仍不确定。我们目前的工作揭示了与紫斑牡丹‘树生彭谟’斑块形成密切相关的因素。非斑点色素沉着是通过花青素结构基因的沉默来防止的，其中PrF3H、PrDFR和PrANS是三个主要基因。我们将两个 R2R3-MYB 定性为分别控制花青素早期和晚期生物合成途径的关键转录因子。PrMYBa1 属于 MYB SG7（亚组 7），被发现可通过与 SG5 成员 PrMYBa2 相互作用形成“MM”复合物来激活 EBG（早期生物合成基因）PrF3H。SG6 成员 PrMYBa3 与两个 SG5 (IIIf) bHLH 相互作用，协同激活 LBG（晚期生物合成基因）PrDFR 和 PrANS，这对于花瓣斑点中花青素的积累至关重要。斑点和非斑点之间 PrANS 和 PrF3H 启动子的甲基化水平的比较表明高甲基化和基因沉默之间的相关性。花发育过程中 PrANS 启动子的甲基化动态揭示了早期潜在的去甲基化反应，该反应可能导致 PrANS 仅在斑点区域的特殊表达。我们认为结构基因启动子的转录激活和DNA甲基化的协同作用可能与花瓣斑病的形成密切相关。