Light and COP1 regulate level of overexpressed DET1 protein

de-etiolated 1 (det1) and constitutive photomorphogenic 1 (cop1) were initially identified as constitutively photomorphogenic Arabidopsis mutants, exhibiting light-grown phenotypes in the dark. Subsequently, both were shown to be components of Damaged DNA Binding protein 1 (DDB1)/CULLIN4-type complexes. Arabidopsis has two DDB1 homologues, DDB1A and DDB1B, and DDB1A mutants enhance det1 phenotypes. Here we examine ddb1a cop1 double mutants and find that ddb1a weakly enhances some cop1 phenotypes but not others, suggesting developmental regulation of COP1-DDB1A interaction. DET1 loss of function strongly enhances cop1 phenotypes. Here we show that MycDET1 overexpression also enhances cop1 phenotypes, thus MycDET1 overexpression in cop1 mutants also generates loss of function effects. Finally, the effect of the cop1 mutant background on the biochemical properties of MycDET1 was examined. MycDET1 levels were found to be lower in the dark than in the light and this difference required COP1. In summary, both DDB1A loss of function and MycDET1 overexpression enhance cop1 phenotypes, while cop1 mutants fail to exhibit light regulation of MycDET1 levels.