The COP1W467 tryptophan residue in the WD40 domain is essential for light- and temperature-mediated hypocotyl growth and flowering in Arabidopsis

Abstract

COP1 is the essential protein that integrates various environmental and hormonal cues to control plant growth and development at multiple levels. COP1 is a RING-finger-type E3 ubiquitin ligase that acts as a potent repressor of photomorphogenesis and flowering by targeting numerous substrates for ubiquitination and promoting their proteolysis via the 26S proteasome system. The WD40 repeat domain with conserved amino acid residues was shown to be essential for interacting with its targets. However, the role of these amino acids in regulating hypocotyl growth and flowering in response to varying light and temperatures remains unknown. Here, we show that tryptophan amino acid at the position 467 residue (COP1^W467) is relevant in mediating the interaction with its targets to regulate the COP1-mediated proteolysis. The COP1^W467 plays a critical role in inducing growth responses in shade light by interacting and degrading HY5, a crucial negative regulator of shade-avoidance response (SAR). Moreover, COP1^W467 integrates warm ambient temperature signals to promote hypocotyl growth by increasing PIF4 and decreasing HY5 protein stability. Finally, we found that COP1^W467 is important in inhibiting flowering under a short-day photoperiod, likely through interacting with CO for degradation. Together, this study highlights that the COP1^W467 residue is essential to regulate seedling photomorphogenesis, SAR, thermomorphogenesis and flowering for the fine adjustment of plant growth and development under dynamic light and temperature conditions.