The plant UV-B photoreceptor UVR8 plays an important role in UV-B acclimation and survival. UV-B absorption by homodimeric UVR8 induces its monomerization and interaction with the E3 ubiquitin ligase COP1, leading ultimately to gene expression changes. UVR8 is inactivated through redimerization, facilitated by RUP1 and RUP2. Here, we describe a novel semi-dominant, hyperactive allele, namely uvr8-17D, that harbors a glycine-101 to serine mutation. UVR8G101S-overexpression led to weak constitutive photomorphogenesis and extreme UV-B responsiveness. UVR8G101S was observed to be predominantly monomeric in vivo and, once activated by UV-B, was not efficiently inactivated. Analysis of a UVR8G101S crystal structure revealed the distortion of a loop region normally involved in stabilization of the UVR8 homodimer. Plants expressing a UVR8 variant combining G101S with the previously described W285A mutation exhibited robust constitutive photomorphogenesis. This work provides further insight into UVR8 activation and inactivation mechanisms, and describes a genetic tool for the manipulation of photomorphogenic responses.

中文翻译：

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组成性单体UVR8感光等位基因赋予增强的UV-B光形态发生能力

植物UV-B感光体UVR8在UV-B适应和生存中起着重要作用。同型二聚体UVR8吸收UV-B诱导其单体化并与E3泛素连接酶COP1相互作用，最终导致基因表达变化。在RUP1和RUP2的帮助下，UVR8通过重新均衡化而失活。在这里，我们描述了一种新型的半显性，过度活跃的等位基因，即uvr8-17D，它携带着甘氨酸101到丝氨酸的突变。UVR8G101S-过表达导致弱的组成型光形态发生和极端的UV-B响应。观察到UVR8G101S在体内主要是单体，一旦被UV-B激活，就不能有效地灭活。对UVR8G101S晶体结构的分析表明，通常与UVR8同型二聚体稳定有关的环区的变形。表达结合了G101S和先前描述的W285A突变的UVR8变体的植物表现出强大的组成型光形态发生。这项工作提供了进一步了解UVR8激活和失活机制，并描述了一种用于操纵光形态发生反应的遗传工具。