Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280-3... more Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280-315 nm) are mediated by the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8). Beyond our understanding of the molecular mechanisms of UV-B perception by UVR8, there is still limited information on how the UVR8 pathway functions under natural sunlight. Here, wild-type Arabidopsis (Arabidopsis thaliana) and the uvr8-2 mutant were used in an experiment outdoors where UV-A (315-400 nm) and UV-B irradiances were attenuated using plastic films. Gene expression, PYRIDOXINE BIOSYNTHESIS1 (PDX1) accumulation, and leaf metabolite signatures were analyzed. The results show that UVR8 is required for transcript accumulation of genes involved in UV protection, oxidative stress, hormone signal transduction, and defense against herbivores under solar UV. Under natural UV-A irradiance, UVR8 is likely to interact with UV-A/blue light signaling pathways to moderate UV-B-driven transcript and PDX1 accumulation. UVR8 both positively and negatively affects UV-A-regulated gene expression and metabolite accumulation but is required for the UV-B induction of phenolics. Moreover, UVR8-dependent UV-B acclimation during the early stages of plant development may enhance normal growth under long-term exposure to solar UV.
The recently identified plant photoreceptor UVR8 triggers regulatory changes in gene expression i... more The recently identified plant photoreceptor UVR8 triggers regulatory changes in gene expression in response to ultraviolet-B (UV-B) light via an unknown mechanism. Here, crystallographic and solution structures of the UVR8 homodimer, together with mutagenesis and far-UV circular dichroism spectroscopy, reveal its mechanisms for UV-B perception and signal transduction. βpropeller subunits form a remarkable, tryptophan-dominated, dimer interface stitched together by a complex salt-bridge network. Salt-bridging arginines flank the excitonically coupled cross-dimer tryptophan "pyramid" responsible for UV-B sensing. Photoreception reversibly disrupts salt bridges, triggering dimer dissociation and signal initiation. Mutation of a single tryptophan to phenylalanine re-tunes the photoreceptor to detect UV-C wavelengths. Our analyses establish how UVR8 functions as a photoreceptor without a prosthetic chromophore to promote plant development and survival in sunlight. UVR8 (UV RESISTANCE LOCUS 8) orchestrates the expression of over 100 genes in Arabidopsis in response to UV-B wavelengths (280-315 nm) (1-4). The uvr8 mutant exhibits UV-B sensitivity from decreased expression of genes conferring UV-protection (1, 5). UV-B exposure promotes both rapid UVR8 accumulation in the nucleus (6), where the protein binds chromatin via histones (1, 7), and interaction with COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1) to initiate transcriptional responses (3,
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Papers by G. Jenkins