Flavonols are important active ingredients that are found in abundance in Dendrobium officinale. Research on flavonol biosynthesis currently focuses on the more ubiquitous kaempferol and quercetin, but little is known on the biosynthesis of myricetin. Notably, flavonol synthase (FLS), which is responsible for the biosynthesis of flavonols, has not yet been identified. In this study, we isolated a flavonol synthase, DoFLS1, from Dendrobium officinale. DoFLS1 harbors conserved 2-oxoglutarate-dependent dioxygenase-specific and FLS-specific motifs. DoFLS1 is a cytoplasmic protein. DoFLS1 was universally expressed in roots, stems, and leaves of juvenile and adult D. officinale plants. DoFLS1 expression was strongly correlated in juvenile and adult D. officinale plants (R2 = 0.86 and 0.98, respectively; p < 0.01) with the average of corresponding flavonol levels. Transgenic Arabidopsis thaliana expressing DoFLS1 exhibited a 1.24-fold increase in flavonol content and a 25.78% decrease in anthocyanin content compare to wild-type plants, possibly resulting from a 78.61% increase in myricetin level. Moreover, the loss of anthocyanin was attributed to decreased expression of dihydroflavonol reductase (DFR) and anthocyanidin synthase (ANS) genes in transgenic A. thaliana that expressed DoFLS1. DoFLS1 also complemented the deficiency in flavonol of the A. thaliana fls1-3 mutant, which had reduced anthocyanin but increased flavonol content relative to the fls1-3 mutant. In addition, DoFLS1 was significantly upregulated after treatment with cold, drought or salicylic acid. These findings provide genetic evidence for the involvement of DoFLS1 in the biosynthesis of flavonol and in response to abiotic stresses.

中文翻译：

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铁皮石斛DoFLS1的异位表达增强拟南芥黄酮醇积累和非生物胁迫耐受性

黄酮醇是重要的活性成分，在铁皮石斛中大量存在。目前对黄酮醇生物合成的研究主要集中在更普遍的山奈酚和槲皮素上，但对杨梅素的生物合成知之甚少。值得注意的是，负责黄酮醇生物合成的黄酮醇合酶 (FLS) 尚未被鉴定。在这项研究中，我们从铁皮石斛中分离出一种黄酮醇合酶 DoFLS1。DoFLS1 具有保守的 2-酮戊二酸依赖性双加氧酶特异性和 FLS 特异性基序。DoFLS1 是一种细胞质蛋白。DoFLS1 在 D. officinale 植物的幼年和成年植物的根、茎和叶中普遍表达。DoFLS1 表达在 D. officinale 幼年和成年植物中密切相关（R2 分别为 0.86 和 0.98；p < 0。01) 与相应黄酮醇水平的平均值。与野生型植物相比，表达 DoFLS1 的转基因拟南芥黄酮醇含量增加了 1.24 倍，花青素含量减少了 25.78%，这可能是由于杨梅素水平增加了 78.61%。此外，花青素的丢失归因于表达 DoFLS1 的转基因拟南芥中二氢黄酮醇还原酶 (DFR) 和花青素合酶 (ANS) 基因的表达降低。DoFLS1 还补充了拟南芥 fls1-3 突变体黄酮醇的缺乏，相对于 fls1-3 突变体，拟南芥 fls1-3 突变体减少了花青素但增加了黄酮醇含量。此外，用寒冷、干旱或水杨酸处理后，DoFLS1 显着上调。