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Plant phytochromes are well-studied photoreceptors that sense red and far-red light, regulating photomorpho- genic development. Molecular signaling mechanisms of phytochrome A (phyA) and phyB largely overlap, especially in regulation of PHYTOCHROME-INTERACTING FACTORs (PIFs) and E3 ligase complexes composed of CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and SUPPRESSORs OF phyA-105 (SPAs). However, the differences in their molecular signaling mechanisms remain unclear. Constitutively active mutants of phyB (YVB) and NLS-fused phyA (YVA:NLS) mediate light-independent seedling development, leading to constitutive photomorphogenic (cop) phenotypes in their transgenic Arabidopsis plants. Interestingly, YVB interacted with PIF3 independently of light, but YVA showed little interaction. In this study, we investigated distinct signaling mechanisms underlying the similar cop phenotypes given by YVB and YVA:NLS. Our findings indicated that YVA efficiently inactivate the COP1/SPA complex, leading to accumulation of ELONGATED HYPOCOTYL 5 (HY5) and subsequent expression of its target genes HY5 and HYH. YVB induced light-independent PIF3 and PIF1 degra- dation, in addition to HY5 accumulation. Moreover, co-expression of PIF3 in the YVB plant significantly attenuated the cop phenotypes, but minimal effects were observed in the YVA:NLS plant. In particular, PIF3 negatively regulated the interaction between YVB and COP1, which decreased HY5 accumulation in the YVB plant co-expressing PIF3. Furthermore, when transferred from light to dark, PIF3 was highly accumulated in phyB-5, whereas HY5 is degraded faster in phyA-201 compared to that in Ler. Collectively, our results suggest HY5 accumulation as the molecular bases for the cop phenotypes and also indicate that phyB is more important for regulating PIF3, whereas phyA effectively inactivates the COP1/SPA complex relative to PIF3 degradation. 

Abstract We present a background model for dark matter searches using an array of NaI(Tl) crystals in the COSINE-100 experiment that is located in the Yangyang underground laboratory. The model includes background contributions from both internal and external sources, including cosmogenic radionuclides and surface $$^{210}$$ 210 Pb contamination. To build the model in the low energy region, with a threshold of 1 keV, we used a depth profile of $$^{210}$$ 210 Pb contamination in the surface of the NaI(Tl) crystals determined in a comparison between measured and simulated spectra. We also considered the effect of the energy scale errors propagated from the statistical uncertainties and the nonlinear detector response at low energies. The 1.7 years COSINE-100 data taken between October 21, 2016 and July 18, 2018 were used for this analysis. Our Monte Carlo simulation provides a non-Gaussian peak around 50 keV originating from beta decays of bulk $$^{210}$$ 210 Pb in a good agreement with the measured background. This model estimates that the activities of bulk $$^{210}$$ 210 Pb and $$^{3}$$ 3 H are dominating the background rate that amounts to an average level of $$2.85\pm 0.15$$ 2.85 ± 0.15  counts/day/keV/kg in the energy region of (1–6) keV, using COSINE-100 data with a total exposure of 97.7 kg $$\cdot $$ · years.