cop1: a regulatory locus involved in light-controlled development and gene expression in Arabidopsis.

Light signals from the environment are perceived by specific regulatory photoreceptors in plants and are transduced by unknown mechanisms to genes that control growth and development. We have identified a genetic locus in Arabidopsis thaliana, which appears to play a central role in this transduction process. Mutations in this locus, designated cop1 (constitutively photomorphogenic), result in dark-grown seedlings with the morphology of wild-type seedlings grown in the light. In addition, these mutations lead to constitutive expression of an array of normally light-regulated genes in dark-grown seedlings and in light-grown adult plants placed in darkness. Promoter-reporter fusion constructs of some of these genes are constitutively expressed in dark-grown transgenic cop1 seedlings, indicating that the aberrant behavior of these genes results primarily from aberrant modulation of their promoter activities in the mutant. In contrast, light control of seed germination and diurnal control of cab gene expression is normal in the cop1 mutants. Because these mutations are recessive, we conclude that in seedlings and adult plants, the wild-type cop1 gene product normally acts in darkness to repress the expression of genes involved in the dark-adaptive developmental and that regulatory photoreceptors act to reverse this action upon exposure to light. However, photocontrol of seed germination and diurnal rhythms is apparently exerted via one or more separate pathways not involving the cop1 product. one or more separate pathways not involving the cop1 product.