Flavonoids are extensively distributed secondary metabolites in land plants. They play a critical role in plant evolution from aquatic to terrestrial and plant adaption to ultraviolet radiation. However, the downstream branching pathway of flavonoids and its regulatory mechanism in bryophytes, which are the most ancient of terrestrial plants, remain unclear. Here, a type I flavone synthase (PnFNSI) was characterized from the Antarctic moss Pohlia nutans. PnFNSI was primarily distributed in the cytoplasm, as detected by subcellular localization. PnFNSI could catalyze the conversion of naringenin to apigenin with an optimal temperature between 15 and 20 °C in vitro. Overexpression of PnFNSI in Arabidopsis alleviated the growth restriction caused by naringenin and accumulated apigenin product. PnFNSI-overexpressing plants showed enhanced plant tolerance to drought stress and UV-B radiation. PnFNSI also increased the enzyme activities and gene transcription levels of reactive oxygen species (ROS) scavengers, protecting plants against oxidative stress. Moreover, overexpression of PnFNSI enhanced the flavone biosynthesis pathway in Arabidopsis. Therefore, this moss FNSI-type enzyme participates in flavone metabolism, conferring protection against drought stress and UV-B radiation.

中文翻译：

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苔藓黄酮合酶I正向调节植物对干旱胁迫和UV-B辐射的耐受性

类黄酮是陆生植物中广泛分布的次生代谢物。它们在植物从水生到陆生的进化以及植物对紫外线辐射的适应中发挥着关键作用。然而，最古老的陆生植物苔藓植物中黄酮类化合物的下游分支途径及其调控机制仍不清楚。在这里，从南极苔藓 Pohlia nutans 中表征了 I 型黄酮合酶 (PnFNSI)。亚细胞定位检测到 PnFNSI 主要分布在细胞质中。PnFNSI 可催化柚皮素转化为芹菜素，体外最佳温度为 15 至 20 °C。PnFNSI 在拟南芥中的过度表达减轻了柚皮素和芹菜素积累产物引起的生长限制。PnFNSI 过表达的植物表现出增强的植物对干旱胁迫和 UV-B 辐射的耐受性。PnFNSI 还增加了活性氧 (ROS) 清除剂的酶活性和基因转录水平，保护植物免受氧化应激。此外，PnFNSI 的过表达增强了拟南芥中的黄酮生物合成途径。因此，这种苔藓 FNSI 型酶参与黄酮代谢，提供对干旱胁迫和 UV-B 辐射的保护。