Functional Characterization of OsCSN1 in the Agronomic Trait Control of Rice Seedlings Under Far-Red Light.

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 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 (GA) 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.