Xi Huang: Dual-source nuclear monomers of UV-B light receptor direct photomorphogenesis in Arabidopsis
Summary: The ultraviolet (UV)-B wavelength (280-315 nm) is an indispensible component of the sunlight that reaches the earth surface. Long-wavelength and low-fluence UV-B specifically induces plant photomorphogenesis, which is characterized by the inhibition of hypocotyl elongation, the promotion of anthocyanin accumulation, and eventually the tolerance against UV-B stress. In Arabidopsis thaliana, UV-B light is perceived by UV RESISTANCE LOCUS 8 (UVR8), a plant-specific chromoprotein. UVR8 forms a symmetrichomodimer in the absence of UV-B light. The tryptophan residues on the surface of the UVR8 dimer serve as the intrinsic chromophore to sense UV-B light. Upon UV-B irradiation, the homodimeric interface, which is stabilized by arginine residues, is disrupted, leading to the monomerization of UVR8. UVR8 is present in both the cytoplasm and the nucleus, and UV-B treatment stimulates the accumulation of UVR8 in the nucleus. However, it is not clear how UV-B regulates the subcellular localization and physiological activity of UVR8. In this study, we explore the mechanism of the build-up of the nuclear UVR8 pool, dissect physiological roles of subcellular UVR8, and reveal positive and negative regulators of UVR8 localization in the photomorphogenic UV-B signaling process.