The dual role of the ubiquitin–proteasome system in photomorphogenesis

The ubiquitin-proteasome system (UPS) represents a highly conserved protein degradation pathway that plays an essential role in maintaining the homeostasis of cellular proteins. This system ensures precise regulation of key regulators within the light signaling pathway, thereby enabling plants to dynamically switch between skotomorphogenesis (growth in the dark) and photomorphogenesis (growth in the light). In darkness, the negative E3 ligases (e.g. CRL4COP1-SPA) target photomorphogenesis-promoting regulators (e.g. ELONGATED HYPOCOTYL5) for ubiquitination and degradation, consequently repressing photomorphogenesis. Conversely, under light conditions, the positive E3 ligases (e.g. CRL1EBF1/2) promote the ubiquitination and degradation of photomorphogenesis-inhibitory regulators (e.g. phytochrome-interacting factors), ensuring proper seedling photomorphogenic development. This mini-review provides a concise overview of the ubiquitin-proteasome system in plants, focusing on recent advances in understanding the role of the UPS in regulating photomorphogenesis. Additionally, we highlight current challenges in further exploring the role of the UPS in photomorphogenesis.