Investigation of light-induced SPA2 degradation and COP1-SPA inactivation in Arabidopsis thaliana

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Light is essential for photoautotrophic life, providing energy and information crucial for plant development. During germination, light significantly influences plant growth. The COP1-SPA E3 ubiquitin ligase complex plays a key role as a central repressor of photomorphogenesis by degrading transcription factors necessary for light responses. This complex's activity is regulated by photoreceptors that help inactivate it. Arabidopsis thaliana contains four SPA proteins, each with unique and overlapping roles in light signal transduction. Notably, SPA2 acts as a strong suppressor of photomorphogenesis in darkness and is heavily regulated by light exposure. When seedlings receive light, SPA2 is rapidly degraded, leading to the inactivation of the COP1-SPA complex. This degradation is thought to stem from interactions with phytochrome photoreceptors and relies on COP1's ubiquitination activity. Research indicates that SPA2 degradation is linked to the CULLIN4-based E3 ligase activity, particularly the CUL4COP10-DET1-DDB1 (CDD) complex, which significantly affects SPA2 stability. A new helical motif in SPA2 may facilitate its interaction with DDB1. Additionally, phytochrome A is crucial for SPA2 degradation, and specific interaction sites within SPA2 have been identified. Transgenic lines lacking certain SPA2 regions showed no degradation in light, and those missing the functional N-terminus displayed skotomorphogenic phenotypes, in