Abstract
Arabidopsis COP1 has been reported to localize in nucleus and acts as ubiquitin E3 ligase to target photomorphogenesis-promoting transcription factor degradation via 26S proteasome pathway. To examine the relationship between nuclear localization and photomorphogenesis repressive activity, GFP-COP1 and GFP-COP1 (NLS mut) fusion genes were constructed and introduced into Arabidopsis. NLS was mutated in the latter to prevent nuclear import of GFP-COP1. Their overexpression didn't cause significant biological effects on skotomorphogenesis, though cotyledon expansion observed in both transgenic plants irrespective to wild type NLS or mutated NLS. Overexpressors were crossed to cop1-4 mutant, and the phenotypes of their F2 populations were examined. From segregation data, it appears that GFP-COP1 partially complements cop1-4 but GFP-COP1 (NLS mut) doesn't. This partial complementation is mostly on cotyledon phenotypes, but not on hypocotyl phenotypes. This might be interpreted as cotyledon folding and hypocotyl elongation in darkness require distinct threshold or different aspect of COP1 activity.
