The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is involved in various regulations during plant development. The CSN is a highly conserved protein complex with nine subunits, and CSN1 acts in a network of signaling pathways critical for plant development. Although CSN1 has been widely studied in Arabidopsis thaliana, there have been few investigations on CSN1 in rice. In this paper, using the CRISPR/Cas9 system, CSN1 was edited from Oryza sativa subsp. japonica (rice). After screening out the OsCSN1 knockout mutant and OsCSN1 reduce mutant, the phenotype and protein expression were identified under different light conditions. Experiments showed that in OsCSN1 knockout mutant and OsCSN1 reduce mutant, the SLR1 protein was rapidly degraded at the rice seedling. In this study, the OsCSN1 acted as a negative regulator to affect seedling growth and development through CUL4-based E3 ligase, which is involved in the degradation of SLR1 in the GA signaling pathway. However, its direct target and mechanism of action are not clear.

The COP9 signalosome (CSN) is a conserved protein complex, with CSN1 being one of the largest and most important subunits in the COP9 complex. To investigate the N-terminus function of OsCSN1, we edited the N-terminus of OsCSN1 and found that the mutant of OsCSN1 with 102 amino acids missing at the N-terminus showed insensitivity to red light in terms of the embryonic sheath, stem elongation, and main-root elongation. Moreover, the mutant was able to produce, develop, and bear fruit normally. The research results indicate that OsCSN1 is a negative regulator of stem elongation in rice seedlings regulated by red light. Under red-light treatment, OsCSN1 assembles into CSN, which degrades SLR1 through de NEDDylation, affecting PIL11 activity and ultimately inhibiting stem elongation. OsCSN1 also plays an important regulatory role in the inhibition of rice embryonic sheath elongation under red light. By regulating the degradation of SLR1 and PIL14 through the ubiquitin/26S protease pathway, the elongation of the embryonic sheath is ultimately inhibited. OsCSN1 forms a COP9 complex and is modified with RUB/NEDD8 of the E3 ligase of CUL1 to promote the degradation of SLR1 and PIL14, ultimately affecting the elongation of the embryonic sheath. The regulatory domain is located at the N-terminus of CSN1.

The COP9 signalosome (CSN) is a highly conserved multi-subunit protein complex, with CSN1 being its largest and most conserved subunit. The N-terminal function of CSN1 plays a pivotal and intricate role in plant photomorphogenesis and seedling development. Moreover, CSN is essential for far-red light-mediated photomorphogenesis in seedlings, but the function of OsCSN1 in seedling growth and development under far-red light conditions has not been determined. This study investigates the function of OsCSN1 under far-red light through phenotypic analysis of wild type and OsCSN1 mutant seedlings. Additionally, the effect of the N-terminal region of OsCSN1 on rice seedling growth and development was examined. The addition of exogenous hormone gibberellin (GA3) and gibberellin synthesis inhibitor paclobutrazol (PAC) resulted in notable changes in phenotypes and the expression of key proteins, including CUL4 and SLR1. The findings indicate that OsCSN1 functions as a positive regulator of plant height under far-red light and inhibits root elongation. Under far-red light, OsCSN1 integrates into the COP9 complex and regulates the nuclear localization of COP1. Through its interaction with CUL4 in the CULLIN-RING family, OsCSN1 facilitates the ubiquitin-mediated degradation of SLR1, thereby influencing the growth of rice seedlings. The regulatory function of OsCSN1 in seedling growth and development under far-red light predominantly relies on the 32 amino acids of its N-terminal region. The results of this study can provide new ideas for rice breeding and genetic improvement. Based on the study of key regulatory factors such as OsCSN1, new varieties that can make better use of far-red light signals can be cultivated to enhance crop adaptability and productivity.

The key flavonoid biosynthesis-related genes and their molecular features in rice have not been comprehensively and systematically characterized. In this study, we investigated the glumes of OsCSN1 mutants and OsCSN2 mutants and found the changes in the total flavonoid contents of the OsCSN2 mutants to be more pronounced than those of the OsCSN1 mutants and the changes in the anthocyanin contents of the OsCSN1 mutants to be more pronounced than those of the OsCSN2 mutants. In addition, key genes related to flavonoid synthesis, OsCHI, showed a more pronounced up-regulation trend, and the OsDFR gene, which encodes a precursor enzyme for anthocyanin synthesis, showed a clear down-regulation trend. And yeast two-hybrid experiments showed that OsCSN1 and OsCSN2 had the ability to interact with OsCUL4. In summary, OsCSN1 and OsCSN2 may regulate the metabolism of flavonoids in rice through CUL4-based E3 ligase, and the two subunits play different roles, laying a foundation for the study of the mechanism of flavonoid metabolism in monocotyledonous plants.

Blue light is a significant environmental cue influencing plant photomorphogenesis and regulating plant growth and development. The COP9 signaling complex (CSN), a multi-subunit protein complex, plays a pivotal role in regulating photomorphogenesis, with CSN2 being identified as a key subunit essential for the assembly and function of the CSN. This study investigated the role of OsCSN2 in rice under blue-light conditions. Utilizing OsCSN2 knockout (KO) mutant plants and transgenic overexpression (OE) lines for wild-type (WT) and mutated versions of OsCSN2, we observed significant suppression of the overall seedling phenotype under blue light, indicating that OsCSN2 acts as a negative regulator of blue light-mediated morphogenesis. Further analysis revealed that exogenous application of gibberellin (GA₃) and the GA synthesis inhibitor paclobutrazol (PAC) modulated seedling elongation in response to blue light, particularly affecting plant height, coleoptile, and first incomplete leaf length without altering root growth. This suggests that OsCSN2 mediates the inhibitory effects of blue light on aboveground development through the gibberellin signaling pathway. On day 9, the analyses of endogenous GA₃ levels combined with Western blotting (WB) and quantitative real-time PCR (qRT-PCR) revealed that OsCSN2 senses blue light signals through cryptochrome 2 (CRY2), influences the expression of COP1 and BBX14, and highlights its role in the photoreceptive signaling pathway. This regulation ultimately influences the degradation of SLR1 within the GA signaling pathway, affecting rice seedling growth and development. Our findings also highlight the differential roles of OsCSN1 and OsCSN2 within the CSN in modulating rice seedling photomorphogenesis, thereby providing new insights into the intricate regulatory mechanisms governing plant responses to blue light.

CSN2, a highly conserved subunit of the COP9 signalosome (CSN), serves as the primary binding site for Cullin in the CSN complex. This interaction, dependent on lysine residues, positions CSN2 as a key player in approximately 20% of CRL-mediated ubiquitination reactions, a critical regulatory pathway for growth, development, and cellular processes in eukaryotes. While the role of CSN2 in human cells has been partially characterized, its function in rice (OsCSN2) remains poorly understood. Building on our previous findings regarding OsCSN2 function under natural light, this study investigates its regulatory mechanisms in rice seedlings under red and far-red light conditions. We demonstrate that under natural light, OsCSN2 mainly affects rice GA homeostasis by regulating the expression of SLR1 and influences rice photomorphogenesis by regulating the expression of the COP1-HY5 complex, thereby controlling rice growth through two pathways. Unlike under natural light, under red light, OsCSN2 promotes the expression of OsGID1, enhances the interaction between OsGID1 and OsSLR1, and promotes GA accumulation and OsPIL14 expression, leading to rice stem growth and inhibition of coleoptile elongation. Under far-red light, OsCSN2 mainly promotes the expression of OsCOP1, increasing the formation of the COP1-HY5 complex, which inhibits photomorphogenesis and coleoptile elongation. Lysine site mutations in OsCSN2 affect the interaction between the OsCSN complex and CRLs, regulating CRL-mediated ubiquitination reactions, promoting the ubiquitin-mediated degradation of OsSLR1 and OsCOP1, and thus promoting rice growth. These findings not only elucidate the functional roles of OsCSN2 in rice growth regulation but also provide valuable genetic resources for breeding rice varieties with enhanced agronomic traits.