Abstract
Plants undergo contrasting developmental programs in dark and light. Photomorphogenesis, a light-adapted programme is repressed in the dark by the synergistic actions of CUL4(COP1-SPA) E3 ubiquitin ligase and a subset of basic helix-loop-helix transcription factors called phytochrome interacting factors (PIFs). To promote photomorphogenesis, light activates the phytochrome family of sensory photoreceptors, which inhibits these repressors by poorly understood mechanisms. Here, we show that the CUL4(COP1-SPA) E3 ubiquitin ligase is necessary for the light-induced degradation of PIF1 in Arabidopsis. The light-induced ubiquitylation and subsequent degradation of PIF1 is reduced in the cop1, spaQ and cul4 backgrounds. COP1, SPA1 and CUL4 preferentially form complexes with the phosphorylated forms of PIF1 in response to light. The cop1 and spaQ seeds display strong hyposensitive response to far-red light-mediated seed germination and light-regulated gene expression. These data show a mechanism by which an E3 ligase attenuates its activity by degrading its cofactor in response to light.
Highlights
Plants undergo contrasting developmental programs in dark and light
PIF1 directly interacts with COP1 and SPA complex and acts as a cofactor of COP1 E3 ubiquitin ligase to synergistically degrade the positively acting factor HY5 to repress photomorphogenesis in the dark[7]
Because PIF1 formed a complex with COP1 and SPA1, components of the E3 ubiquitin ligases in the dark[7], we examined whether the CUL4COP1–SPA E3 ubiquitin ligases play a role in the light-induced degradation of PIF1 in Arabidopsis
Summary
COP1 and SPA complex with CUL4 promote degradation of PIF1. Because PIF1 formed a complex with COP1 and SPA1, components of the E3 ubiquitin ligases in the dark[7], we examined whether the CUL4COP1–SPA E3 ubiquitin ligases play a role in the light-induced degradation of PIF1 in Arabidopsis. PIF1 is slightly more stable in cul[], a weak allele of cul[4] compared with wild-type seedlings under light (Supplementary Fig. 1) Among all these mutants, both spaQ and cul4cs displayed the slowest rate of degradation of PIF1. PIF1 is degraded in the spaQ background under these conditions; the rate of degradation is much slower in the spaQ compared with other mutants (Supplementary Fig. 5) These data suggest that the CUL4COP1–SPA E3 ubiquitin ligase regulates PIF1 levels during dark to light transition. The light-induced degradation of phyA is unaffected in the cul4cs, cop[1], spaQ backgrounds (Supplementary Fig. 7) These data suggest that, unlike PIF3 and phyB23, PIF1 and phyA may not be co-degraded through the CUL4COP1–SPA E3 ubiquitin ligase complexes.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
