Genetic interactions of Arabidopsis thaliana damaged DNA binding protein 1B (DDB1B) with DDB1A, DET1, and COP1.

Damaged DNA Binding protein 1 (DDB1)-CULLIN4 E3 ubiquitin ligase complexes have been implicated in diverse biological processes in a range of organisms. Arabidopsis thaliana encodes two homologs of DDB1, DDB1A, and DDB1B. In this study we use a viable partial loss of function allele of DDB1B, ddb1b-2, to examine genetic interactions with DDB1A, DET1 and COP1. Although the ddb1b-2 ddb1a double mutant is lethal, ddb1a ddb1b-2/+ and ddb1b-2 ddb1a/+ heterozygotes exhibit few developmental phenotypes but do exhibit decreased tolerance of ultraviolet light. In addition, germination in ddb1a and ddb1a ddb1b-2/+ was found to be sensitive to salt and mannitol, and both DDB1 single mutants as well as the heterozygotes exhibited heat sensitivity. DE-ETIOLATED1 (DET1) and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) are negative regulators of light development which interact with DDB1-CUL4 complexes. Although ddb1a strongly enhances det1 phenotypes in both dark- and light-grown seedlings, ddb1b-2 weakly enhanced the det1 short hypocotyl phenotype in the dark, as well as enhancing anthocyanin levels and suppressing the det1 low chlorophyll phenotype in light-grown seedlings. In adults, ddb1a suppresses det1 early flowering and enhances the det1 dwarf phenotype. A similar trend was observed in ddb1b-2 det1 double mutants, although the effects were smaller in magnitude. In cop1 mutants, ddb1b-2 enhanced the cop1-4 short hypocotyl phenotype in dark and light, enhanced anthocyanin levels in cop1-1 in the light, but had no effect in adults. Thus the requirement for DDB1B varies in the course of development, from COP1-specific effects in hypocotyls to DET1-specific in adults.