HDT2-mediated lysine deacetylation promotes phytochrome A degradation during photomorphogenesis in Arabidopsis.

The shift from skotomorphogenesis to photomorphogenesis, a developmental transition in seed plants, involves dramatic proteomic changes. Lysine acetylation (Lys-Ac) is an evolutionarily conserved and recognized post-translational modification that plays a crucial role in plant development. However, its role in seedling deetiolation remains unclear. In this study, we conducted a comparative lysine acetylomic analysis of etiolated Arabidopsis seedlings before and after red (R) light irradiation, uncovering that exposure to R light mainly led to protein lysine deacetylation during seedling deetiolation. Phytochrome A (phyA), a unique far-red (FR) light photoreceptor, was deacetylated at lysine 65 (K65) when etiolated seedlings were moved to light. This residue is a critical ubiquitination site that regulates phyA stability. Moreover, K65 deacetylation facilitates phyA ubiquitination and 26S proteasome-mediated degradation, and is required for the function of phyA in FR light signaling and seedling photomorphogenesis. Furthermore, we identified a plant-specific lysine deacetylase HDT2 that interacts with and deacetylates phyA in the nucleus to promote its ubiquitination and degradation during seedling deetiolation. Genetic analysis revealed that HDT2 is critical for phyA-mediated photomorphogenic growth. Taken together, these findings reveal that lysine deacetylation of phyA by HDT2 plays a crucial role in modulating phyA turnover in response to light, suggesting that Lys-Ac might be central to the reprogramming of plants for photomorphogenic growth.