Dynamic regulation of PIF5 by COP1–SPA complex to optimize photomorphogenesis in Arabidopsis

Abstract

Light signal provides the spatial and temporal information for plants to adapt to the prevailing environmental conditions. Alterations in light quality and quantity can trigger robust changes in global gene expression. In Arabidopsis thaliana, two groups of key factors regulating those changes in gene expression are CONSTITUTIVE PHOTOMORPHOGENESIS/DEETIOLATED/FUSCA (COP/DET/FUS) and a subset of basic helix-loop-helix transcription factors called PHYTOCHROME-INTERACTING FACTORS (PIFs). Recently, rapid progress has been made in characterizing the E3 ubiquitin ligases for the light-induced degradation of PIF1, PIF3 and PIF4; however, the E3 ligase(s) for PIF5 remains unknown. Here, we show that the CUL4 complex is necessary for the red light-induced degradation of PIF5. Furthermore, COP1 and SPA proteins stabilize PIF5 in the dark, but promote the ubiquitination and degradation of PIF5 in response to red light through the 26S proteasome pathway. Genetic analysis illustrates that overexpression of PIF5 can partially suppress both cop1-4 and spaQ seedling de-etiolation phenotypes under dark and red-light conditions. In addition, the PIF5 protein level cycles under both diurnal and constant light conditions, which is also defective in the cop1-4 and spaQ backgrounds. Both cop1-4 and spaQ show defects in diurnal growth pattern. Overexpression of PIF5 partially restores growth defects in cop1-4 and spaQ under diurnal conditions, suggesting that the COP1-SPA complex plays an essential role in photoperiodic hypocotyl growth, partly through regulating the PIF5 level. Taken together, our data illustrate how the CUL4 E3 ligase dynamically controls the PIF5 level to regulate plant development.

Molecular bases for the constitutive photomorphogenic phenotypes in Arabidopsis

“…HY5/HFR1/LAF1 and others) in the dark (Hoecker, 2017). However, a few reports showed that PIFs are less abundant in cop1 mutants (Bauer et al, 2004;Pham et al, 2018a;Shen et al, 2008;Xu et al, 2017;Zhu et al, 2015) and also to a lesser extent in spaQ mutants (Leivar et al, 2008;Ni et al, 2014;Pham et al, 2018a), suggesting that the instability of PIFs contributes to the cop phenotypes of these mutants. Here, we show that the gene expression signature of cop1 and spaQ overlaps with pifQ in the dark, with preferential targeting of PIF direct target genes, suggesting that the cop phenotype of cop1 and spaQ is partly due to a reduced level of PIFs in these backgrounds.…”

“…Previously, we and others showed that the PIF levels in cop1 and spaQ mutants are reduced compared with wild type in the dark (Bauer et al, 2004;Leivar et al, 2008;Pham et al, 2018a;Zhu et al, 2015). To systematically analyze PIF levels without the transcriptional regulation in these mutants, we crossed the overexpression lines of tagged PIF1, PIF3, PIF4 and PIF5 using the constitutively active 35S promoter in cop1-4, TAP-PIF1 and PIF5-Myc in spaQ mutant backgrounds, and performed immunoblots for protein levels.…”

Regulation of diurnal growth: phytochrome interacting factor 5 is degraded by the E3 ubiquitin ligase CUL4COP1‐SPA

“…PIF3 is degraded by CUL3 LRB and PIF4 by CUL3 BOP ; PIF1 is also degraded by CUL1 CTG10 and PIF3 is also degraded by CUL1 EBF1/2 . In the highlighted paper (Pham et al ., 2018b) and as illustrated schematically in the left panel of Figure , Enamul Huq's group demonstrate that CUL4 COP1‐SPA is necessary for the red light‐induced degradation of PIF5.…”

“…PIF3 is degraded by CUL3 LRB and PIF4 by CUL3 BOP ; PIF1 is also degraded by CUL1 CTG10 and PIF3 is also degraded by CUL1 EBF1/2 . In the highlighted paper (Pham et al, 2018b) and as illustrated schematically COP1 SPA COP1 SPA PIF5 Growthpromo ng genes Protein degradation PIF5 Figure 1. Schematic showing that the COP1-SPA complex promotes PIF5 ubiquitination and degradation during early light responses (left panel) but also controls hypocotyl growth under diurnal conditions by stabilizing PIF5, which can then activate the expression of growth-promoting genes at night (right panel).…”

“…PIF3 is degraded by CUL3 LRB and PIF4 by CUL3 BOP ; PIF1 is also degraded by CUL1 CTG10 and PIF3 is also degraded by CUL1 EBF1/2 . In the highlighted paper (Pham et al, 2018b) and as illustrated schematically Figure 1, Enamul Huq's group demonstrate that CUL4 COP1-SPA is necessary for the red lightinduced degradation of PIF5. Enamul Huq has worked on the molecular biology of photomorphogenesis for more than 20 years, first as a postdoc with Peter Quail, at the Plant Gene Expression Center, from 1997 to 2003, where he identified and characterized Arabidopsis PIFs, and since then as a professor at the University of Texas-Austin.…”