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 unclear ^1,2 . 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.