A COMPLEMENT OF 10 ESSENTIAL AND PLEIOTROPIC ARABIDOPSIS COP DET/FUS GENES IS NECESSARY FOR REPRESSION OF PHOTOMORPHOGENESIS IN DARKNESS/

Two genetic screens, one for mutations resulting in photomorphogenic d evelopment in darkness and the other for mutants with fusca phenotype, have thus far identified six pleiotropic Arabidopsis COP/DET/FUS gene s. Here, we characterized representative mutants that define four addi tional pleiotropic photomorphogenic loci and a null mutant allele of t he previously defined DET1 locus. Dark-grown seedlings homozygous for these recessive mutations exhibit short hypocotyls and expanded cotyle dons and are lethal before reaching reproductive development. Dark-gro wn mutant seedlings also display characteristic photomorphogenic cellu lar differentiation and elevated expression of light-inducible genes. In addition, analyses of plastids from dark-grown mutants reveal parti al chloroplast differentiation and absence of etioplast development. R oot vascular bundle cells of light-grown mutant seedlings develop chlo roplasts, suggesting that these FUS gene products are important for su ppression of chloroplast differentiation in light-grown roots. Double- mutant analyses indicate that these pleiotropic cop/det/fus mutations are epistatic to mutations in phytochromes, a blue-light photoreceptor , and a downstream regulatory component, HY5. Therefore, there is a co mplement of at least 10 essential and pleiotropic Arabidopsis genes th at are necessary for repression of photomorphogenic development.