A nuclear pore complex component HOS1 mediates UV-B light-induced UVR8 nuclear localization for activating HY5 cascade in Arabidopsis

Upon ultraviolet-B (UV-B) exposure, the photoreceptor UVR8 translocates to the nucleus and interacts with COP1 to activate downstream transcription factors, notably including HY5. However, the mechanism of UVR8 nuclear import has remained unclear1,2. Here, we identified HOS1, a component of the nuclear pore complex (NPC), as a key mediator of UVR8 nuclear translocation under UV-B conditions. HOS1 directly interacts with UVR8 specifically in response to UV-B, facilitating its efficient import into the nucleus. Consistent with this role, HOS1-deficient mutants exhibit reduced HY5 protein accumulation, compromised UV-B tolerance, and impaired expression of HY5-regulated genes, including those involved in anthocyanin synthesis. These findings reveal a novel role of HOS1 in bridging UV-B perception in the cytoplasm and gene transcriptional activation in the nucleus by enabling UVR8 nuclear import. They highlight a distinct broader role of NPC components in coordinating plant transcriptional response to environmental stimuli.