Low UV-B fluence is a signaling stimulus that regulates various physiological processes and induces photomorphogenic responses in plants. The specific UV-B receptor UVR8 is a key component in these processes. Although UVR8 sequence is conserved, few homologs have been cloned and reported to be functional. Here we show the cloning and functional analysis of Zea mays UVR8 (ZmUVR8). ZmUVR8 presents 73% of identity with AtUVR8, maintaining the key tryptophan responsible of UV-B perception. ZmUVR8 also contains the VP domain, involved in the interaction with the proteins CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1). Whereas UVR8 was expressed in non-irradiated Arabidopsis and maize leaves, after 2 h of UV-B irradiation, its expression was reduced. The expression of chalcone synthase (CHS), involved in flavonoid biosynthesis and regulated by UVR8, was increased in irradiated Arabidopsis and maize leaves. Arabidopsis uvr8-1 null mutant was complemented with ZmUVR8 driven by the CaMV-35S promoter and fused to eGFP. ZmUVR8-eGFP fusion was mainly localized in nuclei of transgenic lines, irrespective of UV-B treatments. UV-B suppressed hypocotyl elongation in wild type (WT) Arabidopsis plants, whereas in uvr8-1 hypocotyl growth was observed. However, hypocotyl elongation was reduced in UV-B irradiated transgenic lines complemented with ZmUVR8. Moreover, CHS and transcription factor HY5 (ELONGATED HYPOCOTYL 5) expression were also restored in these plants. These results confirm that ZmUVR8 is similar enough to AtUVR8 to restore UV-B perception and signaling in Arabidopsis mutant uvr8-1, thus being a functional UV-B photoreceptor. That reinforce the importance of UVR8 as a functional UV-B-responsive regulator in land plants.

中文翻译：

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来自单子叶玉米的 UVR8 光感受器的功能分析

低 UV-B 通量是一种信号刺激，可调节植物的各种生理过程并诱导光形态发生反应。特定的 UV-B 受体 UVR8 是这些过程中的关键组成部分。尽管 UVR8 序列是保守的，但很少有同源物被克隆并报告有功能。在这里，我们展示了玉米 UVR8 (ZmUVR8) 的克隆和功能分析。ZmUVR8 与 AtUVR8 具有 73% 的同一性，保持负责 UV-B 感知的关键色氨酸。ZmUVR8 还包含 VP 结构域，参与与蛋白质 CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) 和 REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) 的相互作用。UVR8 在未照射的拟南芥和玉米叶片中表达，而在 UV-B 照射 2 小时后，其表达降低。查尔酮合酶（CHS）的表达，参与黄酮类生物合成并受 UVR8 调节的 β 受体在受辐照的拟南芥和玉米叶片中增加。拟南芥 uvr8-1 无效突变体与由 CaMV-35S 启动子驱动的 ZmUVR8 互补并与 eGFP 融合。ZmUVR8-eGFP 融合主要位于转基因株系的细胞核中，与 UV-B 处理无关。UV-B 抑制野生型 (WT) 拟南芥植物中的下胚轴伸长，而在 uvr8-1 中观察到下胚轴生长。然而，在补充有 ZmUVR8 的 UV-B 辐照转基因品系中，下胚轴伸长率降低。此外，CHS 和转录因子 HY5（ELONGATED HYPOCOTYL 5）的表达也在这些植物中恢复。这些结果证实 ZmUVR8 与 AtUVR8 足够相似，可以恢复拟南芥突变体 uvr8-1 中的 UV-B 感知和信号传导，因此是一种功能性 UV-B 光感受器。