Targeted destabilization of HY5 during light-regulated development of Arabidopsis

Abstract

Arabidopsis seedlings display contrasting developmental patterns depending on the ambient light. Seedlings grown in the light develop photomorphogenically, characterized by short hypocotyls and expanded green cotyledons. In contrast, seedlings grown in darkness become etiolated, with elongated hypocotyls and dosed cotyledons on an apical hook. Light signals, perceived by multiple photoreceptors and transduced to downstream regulators, dictate the extent of photomorphogenic development in a quantitative manner. Two key downstream components, COP1 and HY5, act antagonistically in regulating seedling development. HY5 is a bZIP transcription factor that binds directly to the promoters of light-inducible genes, promoting their expression and photomorphogenic development. COP1 is a RING-finger protein with WD-40 repeats whose nuclear abundance is negatively regulated by light. COP1 interacts directly with HY5 in the nucleus to regulate its activity negatively. Here we show that the abundance of HY5 is directly correlated with the extent of photomorphogenic development, and that the COP1-HY5 interaction may specifically target HY5 for proteasome-mediated degradation in the nucleus.

COP1 mediates the coordination of root and shoot growth by light through modulation of PIN1- and PIN2-dependent auxin transport in Arabidopsis

“…How this is achieved is still unknown but an attractive possibility is that one of the targets of COP1-mediated degradation might directly activate PIN1 transcription. The bZIP transcription factor LONG HYPOCOTYL 5 (HY5), which is the bestcharacterized target of COP1-mediated proteolysis (Osterlund et al, 2000), would be a good candidate as several functional links between HY5 and auxin have been established (Cluis et al, 2004;Sibout et al, 2006). However, although HY5 binding sites were found in the PIN1 locus , genome-wide expression analyses did not detect significant changes in PIN1 expression in the hy5 mutant (Cluis et al, 2004;Zhang et al, 2011).…”

PSEUDO RESPONSE REGULATORs stabilize CONSTANS protein to promote flowering in response to day length

“…In A. thaliana light‐signaling pathways, COP1 acts as a negative regulator to suppress photomorphogenesis by targeting proteins such as the transcription factor ELONGATED HYPOCOTYL 5 (HY5) for proteasomal degradation during the dark (Osterlund et al , 2000). In the light, phys and crys suppress COP1 function, allowing HY5 to accumulate and promote photomorphogenesis (Osterlund et al , 2000).…”

“…In the light, phys and crys suppress COP1 function, allowing HY5 to accumulate and promote photomorphogenesis (Osterlund et al , 2000). The photoreceptor‐COP1 module also controls CO protein abundance, where phyA, cry1, and cry2 suppress the activity of COP1 to degrade CO thereby allowing CO to accumulate during the day (Zuo et al , 2011; Sarid‐Krebs et al , 2015).…”

Signalling for developmental plasticity

“…For example, in the case of phytochrome A (phyA, X17341), different domains of the molecule participate in the control of pathways that can be dissected genetically by mutations in downstream components: molecularly by the relevant regions of target gene promoters and functionally by the strength of the light signal required to activate the pathway [14,15]. Furthermore, if we rotate the plane of analysis, phyA is known to control transcription via direct interaction with DNA-binding proteins [16] but it is also able to regulate the abundance of transcription factors involved in photomorphogenesis by reducing CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1, Accession number L24437)-mediated targeting to proteasome degradation [17].…”

“…For example, COP1, DE-ETIOLATED 1 (DET1, Accession number L33695) [36,37], and COP9 (Accession number L33695) [38] are nuclear proteins that repress photomorphogenesis in darkness and have animal counterparts. COP1 promotes ubiquitin-mediated proteolysis of a subset of positive regulators, including HY5 [17] and LONG AFTER FAR-RED (LAF1, Accession number Z95744) [39]. Light promotes translocation of COP1 to the cytoplasm allowing de-etiolation, partly through the action of HY5 and LAF1.…”