ARABIDOPSIS COP8, COP10, AND COP11 GENES ARE INVOLVED IN REPRESSION OF PHOTOMORPHOGENIC DEVELOPMENT IN DARKNESS

Wild-type Arabidopsis seedlings are capable of following two developme ntal prog rams: photomorphogenesis in the light and skotomorphogenesis in darkness. Screening of Arabidopsis mutants for constitutive photom orphogenic development in darkness resulted in the identification of t hree new loci designated COP8, COP10, and COP11. Detailed examination of the temporal morphological and cellular differentiation patterns of wild-type and mutant seedlings revealed that in darkness, seedlings h omozygous for recessive mutations in COP8, COP10, and COP11 failed to suppress the photomorphogenic developmental pathway and were unable to initiate skotomorphogenesis. As a consequence, the mutant seedlings g rown in the dark had short hypocotyls and open and expanded cotyledons , with characteristic photomorphogenic cellular differentiation patter ns and elevated levels of light-inducible gene expression. In addition , plastids of dark-grown mutants were defective in etioplast different iation. Similar to cop1 and cop9, and in contrast to det1 (deetiolated ), these new mutants lacked dark-adaptive change of light-regulated ge ne expression and retained normal phytochrome control of seed germinat ion. Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, an d hy5 mutations suggested that these three loci, similar to COP1 and C OP9, act downstream of both phytochromes and a blue light receptor, an d probably HY5 as well. Further, cop8-1, cop10-1, and cop11-1 mutants accumulated higher levels of COP1, a feature similar to the cop9-1 mut ant. These results suggested that COP8, COP10, and COP11, together wit h COP1, COP9, and DET1, function to suppress the photomorphogenic deve lopmental program and to promote skotomorphogenesis in darkness. The i dentical phenotypes resulting from mutations in COP8, COP9, COP10, and COP11 imply that their encoded products function in close proximity, possibly with some of them as a complex, in the same signal transducti on pathway.