Abstract
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.
Highlights
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)
The role of different bands of solar UV in UVR8mediated responses was studied by subjecting wildtype Arabidopsis Landsberg erecta (Ler) and uvr8-2 (Brown et al, 2005) transferred from greenhouse to field conditions under filters used to manipulate UV-A and UV-B irradiance
UVR8 regulates the expression of genes involved in UV protection, defense responses, and the biosynthesis and signaling of JA, salicylic acid (SA), and glucosinolates
Summary
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). Transcriptome analyses of uvr mutants exposed to low fluence rates of UV-B indoors have shown that UVR8 is required for the induction of genes with important functions in UV protection (flavonoid and alkaloid pathways), photorepair of DNA damage induced by UV-B, oxidative stress, chloroplast proteins, and several transcription factors (Brown et al, 2005; Favory et al, 2009). The manner by which UVR8 regulates the accumulation of phenolics and other metabolites under natural sunlight has not yet been studied, and the role of UVR8 and its possible interaction with UV-A/blue light signaling in mediating the UV-A induction of several metabolites is not well understood This information is important for understanding the mechanisms, driven by UVR8 and/or other photoreceptors, that provide solar UV protection in plants. It remains unclear how PDX1 accumulates under natural fluxes of solar UV-A and UV-B radiation and if UVR8 is involved in this process
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