Ubiquitin-specific protease UBP14 stabilizes HY5 by deubiquitination to promote photomorphogenesis in <i>Arabidopsis thaliana</i>

Transcription factor ELONGATED HYPOCOTYL5 (HY5) is the central hub for seedling photomorphogenesis. E3 ubiquitin (Ub) ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) inhibits HY5 protein accumulation through ubiquitination. However, the process of HY5 deubiquitination, which antagonizes E3 ligase-mediated ubiquitination to maintain HY5 homeostasis has never been studied. Here, we identified that <i>Arabidopsis thaliana</i> deubiquitinating enzyme, Ub-SPECIFIC PROTEASE 14 (UBP14) physically interacts with HY5 and enhances its protein stability by deubiquitination. The <i>da3-1</i> mutant lacking UBP14 function exhibited a long hypocotyl phenotype, and UBP14 deficiency led to the failure of rapid accumulation of HY5 during dark to light. In addition, UBP14 preferred to stabilize nonphosphorylated form of HY5 which is more readily bound to downstream target genes. HY5 promoted the expression and protein accumulation of UBP14 for positive feedback to facilitate photomorphogenesis. Our findings thus established a mechanism by which UBP14 stabilizes HY5 protein by deubiquitination to promote photomorphogenesis in <i>A. thaliana</i>.