Prefoldin 3 promotes the turnover of WRKY70 and FHY3 to modulate UV-B-induced hypocotyl growth inhibition in Arabidopsis thaliana.

Ultraviolet-B (UV-B) radiation, a pervasive light stimulus, profoundly influences plant hypocotyl growth through intricate signaling pathways. Although the core UV-B signaling components have been identified, the precise regulatory mechanisms remain elusive. Here, we identify prefoldin 3 (PFD3), an α subunit of the PFD complex, as a novel negative regulator of UV-B-induced hypocotyl growth inhibition in Arabidopsis thaliana. Upon UV-B exposure, PFD3 accumulates and promotes the turnover of WRKY DNA-BINDING PROTEIN 70 (WRKY70) and FAR-RED ELONGATED HYPOCOTYL 3 (FHY3), thereby attenuating their transcriptional activities toward ELONGATED HYPOCOTYL 5 (HY5)/PACLOBUTRAZOL RESISTANCE1 (PRE1) and CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), respectively. These findings delineate two regulatory modules-PFD3-WRKY70-HY5/PRE1 and PFD3-FHY3-COP1-that fine-tune UV-B-mediated inhibition of hypocotyl elongation in a UV RESISTANCE LOCUS 8-dependent manner. Furthermore, we identify amino acid variations in FHY3 from the high-altitude Tibet-0 ecotype of A. thaliana that confer resistance to PFD3-mediated suppression. This genetic adaptation sustains COP1 activation and results in shortened hypocotyls under UV-B radiation in this alpine ecotype. Collectively, our results suggest that allelic variation within these modules enhances adaptation to high-intense UV-B habitats, highlighting the evolutionary significance of these regulatory networks in plant environmental acclimation.