Acts as positive regulator of seedling photomorphogenesis and light-regulated inhibition of hypocotyl elongation, independently and in concert with HY5 and BBX21 (PubMed:18540109, PubMed:18796637, PubMed:18182030, PubMed:21427283). Acts as a positive regulator of de-etiolation and influences chloroplast biogenesis and function through regulation of genes encoding chloroplast proteins (PubMed:18182030). Acts downstream of COP1 and plays an important role in early and long-term adjustment of the shade avoidance syndrome (SAS) responses in natural environments (PubMed:21070414). Regulates the expression of genes responsive to light hormone signals which may contribute to optimal seedling development (PubMed:21427283). Interacts with HY5. A number of isoforms are produced. According to EST sequences. By light. Ubiquitinated by COP1 in vitro (PubMed:18796637). COP1-mediated degradation of BBX22 by the proteasome occurs in the dark and is important for a precise skotomorphogenesis process and optimization of seedling growth under short days conditions (PubMed:21427283). Increased hypocotyl length under short day conditions (PubMed:18796637). Delayed chloroplast development (PubMed:18182030).