Non-damaging ultraviolet B (UV-B) light promotes photomorphogenic development and stress acclimation through UV-B-specific signal transduction in Arabidopsis. UV-B irradiation induces monomerization and nuclear translocation of the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8). However, it is not clear how the nuclear localization of UVR8 leads to changes in global gene expression. Here, we reveal that nuclear UVR8 governs UV-B-responsive transcriptional networks in concert with several previously known transcription factors, including ELONGATED HYPOCOTYL 5 (HY5) and PHYTOCHROME INTERACTING FACTOR 4 (PIF4). Based on the transcriptomic analysis, we identify MYB13 as a novel positive regulator in UV-B-induced cotyledon expansion and stress acclimation. MYB13 is UV-B inducible and is predominantly expressed in the cotyledons. Our results demonstrate that MYB13 protein functions as a transcription factor to regulate the expression of genes involved in auxin response and flavonoid biosynthesis through direct binding with their promoters. In addition, photoactivated UVR8 interacts with MYB13 in a UV-B-dependent manner and differentially modulates the affinity of MYB13 with its targets. Taken together, our results elucidate the cooperative function of the UV-B photoreceptor UVR8 with various transcription factors in the nucleus to orchestrate the expression of specific sets of downstream genes and, ultimately, mediate plant responses to UV-B light.

无害紫外线B（UV-B）通过拟南芥中的UV-B特异性信号转导促进光形态发生发展和应力适应。UV-B辐射诱导UV-B感光体UV RESISTANCE LOCUS 8（UVR8）的单体化和核易位。但是，尚不清楚UVR8的核定位如何导致整体基因表达的变化。在这里，我们揭示了核UVR8与几个先前已知的转录因子（包括长双氢代草酸5（HY5）和植物染色体相互作用因子4（PIF4））共同控制着UV-B响应转录网络。基于转录组分析，我们将MYB13鉴定为UV-B诱导的子叶扩增和逆境驯化的新型正调控剂。马币13是UV-B诱导型的，主要在子叶中表达。我们的结果表明，MYB13蛋白起转录因子的作用，通过与其启动子直接结合，调节生长素应答和类黄酮生物合成中涉及的基因的表达。此外，光活化的UVR8以依赖UV-B的方式与MYB13相互作用，并差异性地调节MYB13及其靶标的亲和力。两者合计，我们的结果阐明了UV-B感光器UVR8与细胞核中各种转录因子的协同功能，以协调下游基因的特定集合的表达，并最终介导植物对UV-B光的反应。