Figure 6.

Conserved COP/DET/FUS Proteins Are Involved in Distinct Light-Regulatory Pathways in Chlamydomonas and Arabidopsis.

(A) In Chlamydomonas, CrPHOT senses high light and induces photoprotection responses. In low light, both the CDD complex and COP1/SPA complex repress high light responses. In high light the activity of these E3 ubiquitin ligases is inhibited, allowing CrCO accumulation and the expression of high light-responsive genes. Under UV-B light, activated CrUVR8 monomers interact with CrCOP1 and induce the accumulation of CrHY5, and thus promote UV-B responses and acclimation.

(B) In Arabidopsis, light-activated photoreceptors inactivate COP/DET/FUS protein complexes, thus allowing the accumulation of photomorphogenesis-promoting regulators such as HY5 to globally activate light-responsive genes and photomorphogenic development. Similarly to Chlamydomonas CrUVR8, Arabidopsis UVR8 senses UV-B light and forms a new complex with the COP1/SPA core apparatus, which indirectly promotes the accumulation of HY5 and photomorphogenic development.