RUP2 facilitates UVR8 redimerization via two interfaces.

The plant UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) exists as a homodimer in its inactive ground state. Upon UV-B exposure, UVR8 monomerizes and interacts with a downstream key regulator, the CONSTITUTIVE PHOTOMORPHOGENIC 1/SUPPRESSOR OF PHYA (COP1/SPA) E3 ubiquitin ligase complex, to initiate UV-B signaling. Two WD40 proteins, REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 directly interact with monomeric UVR8 and facilitate UVR8 ground state reversion, completing the UVR8 photocycle. Here, we reconstituted the RUP-mediated UVR8 redimerization process in vitro and reported the structure of the RUP2-UVR8W285A complex (2.0 Å). RUP2 and UVR8W285A formed a heterodimer via two distinct interfaces, designated Interface 1 and 2. The previously characterized Interface 1 is found between the RUP2 WD40 domain and the UVR8 C27 subregion. The newly identified Interface 2 is formed through interactions between the RUP2 WD40 domain and the UVR8 core domain. Disruption of Interface 2 impaired UV-B induced photomorphogenic development in Arabidopsis thaliana. Further biochemical analysis indicated that both interfaces are important for RUP2-UVR8 interactions and RUP2-mediated facilitation of UVR8 redimerization. Our findings suggest that the two-interface-interaction mode is adopted by both RUP2 and COP1 when they interact with UVR8, marking a step forward in understanding the molecular basis that underpins the interactions between UVR8 and its photocycle regulators.

Structural insight into UV-B-activated UVR8 bound to COP1.

The CONSTITUTIVE PHOTOMORPHOGENIC 1-SUPPRESSOR OF PHYA-105 (COP1-SPA) complex is a central repressor of photomorphogenesis. This complex acts as an E3 ubiquitin ligase downstream of various light signaling transduced from multiple photoreceptors in plants. How the COP1-SPA activity is regulated by divergent light-signaling pathways remains largely elusive. Here, we reproduced the regulation pathway of COP1-SPA in ultraviolet-B (UV-B) signaling in vitro and determined the cryo-electron microscopy structure of UV-B receptor UVR8 in complex with COP1. The complex formation is mediated by two-interface interactions between UV-B-activated UVR8 and COP1. Both interfaces are essential for the competitive binding of UVR8 against the signaling hub component HY5 to the COP1-SPA complex. We also show that RUP2 dissociates UVR8 from the COP1-SPA41-464-UVR8 complex and facilitates its redimerization. Our results support a UV-B signaling model that the COP1-SPA activity is repressed by UV-B-activated UVR8 and derepressed by RUP2, owing to competitive binding, and provide a framework for studying the regulatory roles of distinct photoreceptors on photomorphogenesis.

The Influence Mechanism of Ettringite Crystals and Microstructure Characteristics on the Strength of Calcium-Based Stabilized Soil.

To reveal the influence mechanism of ettringite (AFt) crystals and microstructure characteristics on the strength of calcium-based stabilized soil, the strengths and microscopic properties of seven groups of stabilized soil samples were studied systematically through unconfined compressive strength, scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TG), and Fourier transform infrared spectroscopy (FTIR) testing methods. The results indicate that the strength of the cement-stabilized soil is relatively high because abundant calcium silicate hydrate (CSH) gels coat the outer surface of soil particles to cement together. For the cement-gypsum-stabilized soil, superabundant thick and long AFt crystals make the pores in soil particles larger, and the sample becomes looser, resulting in lower strength than that of the cement-stabilized soil. However, the strength of the cement-gypsum-lime-stabilized soil is slightly stronger than that of the cement-stabilized soil, for the reason that the appropriate amount of fine AFt crystals fill the macropores between soil particles to form a network space structure and sufficient CSH gels cement the soil particles and the AFt crystals network space structure tightly together. It could be suggested that the components of calcium-based stabilizer should consider the optimal production balance between CSH gels and fine AFt crystals.

Degradation of Axial Ultimate Load-Bearing Capacity of Circular Thin-Walled Concrete-Filled Steel Tubular Stub Columns after Corrosion.

This work aimed to investigate the effects of steel tube corrosion on the axial ultimate load-bearing capacity (AULC) of circular thin-walled concrete-filled steel tubular (CFST) members. Circular thin-walled CFST stub column specimens were made of steel tubes with various wall-thicknesses. These CFST column specimens were subjected to an accelerated corrosion test, where the steel tubes were corroded to different degrees of corrosion. Then, these CFST specimens with corroded steel tubes experienced an axial static loading test. Results show that the failure patterns of circular thin-walled CFST stub columns with corroded steel tubes are different from those of the counterpart CFST columns with ordinary wall-thickness steel tubes, which is a typical failure mode of shear bulging with slight local outward buckling. The ultimate strength and plastic deformation capacity of the CFST specimens decreased with the increasing degree of steel corrosion. The failure modes of the specimens still belonged to ductile failure because of the confinement of outer steel tube. The degree of steel tube corrosion, diameter-to-thickness ratio, and confinement coefficient had substantial influences on the AULC and the ultimate compressive strength of circular thin-walled CFST stub columns. A simple AULC prediction model for corroded circular thin-walled CFST stub columns was presented through the regression of the experimental data and parameter analysis.