College of Horticulture, Qingdao Agricultural University, Qingdao, Shandong 266109, China.
State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural University, Hefei, Anhui 230036, China.
J Agric Food Chem. 2020 Dec 23;68(51):15142-15153. doi: 10.1021/acs.jafc.0c05048. Epub 2020 Dec 12.
Anthocyanins and PAs are the two most common flavonoids, which are widely present among diverse species. Great progress has been made in their synthesis and regulation. In this study, we analyzed the metabolic fluxes from their synthetic precursor leucoanthocyanins, which were obtained by overexpression of dihydroflavonol 4-reductase (DFR) and . The unstable product leucocyanidin generated in the CsDFRa enzymatic reaction was easily converted into C-type carbocations under weak acidic conditions, which could be further involved in the synthesis of C-type PAs . Additionally, the metabolites in tobacco overexpressing and DFR and anthocyanidin synthase (ANS) mutants were investigated. In transgenic tobacco, the content of anthocyanins in the petals was greatly increased, but no catechin or PA was detected. In , EC-type carbocation was mainly accumulated in the wild type (WT), and the C-type carbocation was only detected in the mutant. In tea plant, the accumulation of C-type PAs is strong positively correlated with the expression of . In summary, leucocyanidin is not only involved in the synthesis of downstream anthocyanin and epicatechin but also can be converted into C-type carbocation to participate in the synthesis of C-type PAs. Hence, from leucocyanidin, three metabolic fluxes were formed toward catechin, cyanidin, and C-type carbocation. These results enriched the metabolic fluxes of leucoanthocyanins and further elaborated the roles of DFR in the process of C-type PA formation.
花色素苷和 PAs 是两种最常见的类黄酮，广泛存在于不同的物种中。它们的合成和调控已经取得了很大的进展。在这项研究中，我们分析了它们的合成前体——无色花色素苷的代谢通量，这些无色花色素苷是通过过量表达二氢黄酮醇 4-还原酶（DFR）和 获得的。CsDFRa 酶促反应中产生的不稳定产物无色飞燕草素在弱酸性条件下很容易转化为 C 型碳正离子，可进一步参与 C 型 PAs 的合成。此外，还研究了过表达 和 DFR 以及类黄酮 3’-羟化酶（ANS）突变体的烟草中的代谢物。在 转基因烟草中，花瓣中的花色素苷含量大大增加，但未检测到儿茶素或 PA。在 中，EC 型碳正离子主要在野生型（WT）中积累，而 C 型碳正离子仅在 突变体中检测到。在茶树中，C 型 PAs 的积累与 的表达呈强正相关。综上所述，无色飞燕草素不仅参与下游花色素苷和表儿茶素的合成，还可以转化为 C 型碳正离子参与 C 型 PAs 的合成。因此，从无色花色素苷形成了三条代谢通量，分别通向儿茶素、矢车菊素和 C 型碳正离子。这些结果丰富了无色花色素苷的代谢通量，并进一步阐述了 DFR 在 C 型 PA 形成过程中的作用。
