DET1, a negative regulator of light-mediated development and gene expression in arabidopsis,encodes a novel nuclear-localized protein

The mechanisms by which plants integrate light signals to modify endogenous developmental programs are largely unknown. One candidate for a signal transduction component that may integrate light with developmental pathways is the Arabidopsis DET1 gene product. Here we report the positional cloning of the DET1 locus and show that DET1 is a unique nuclear-localized protein. An analysis of a number of det1 mutants indicates that mutants with partial DET1 activity develop as light-grown plants in the dark. det1 null mutants share this phenotype, but also display severe defects in temporal and spatial regulation of gene expression. These results suggest that DET1 acts in the nucleus to control the cell type-specific expression of light-regulated promoters.     

Phenotypic and Genetic Analysis of det2, a New Mutant That Affects Light-Regulated Seedling Development in Arabidopsis

The greening phenotypes produced by recessive mutations in a gene designated de-etiolated-2 (DET2) are described. Recessive mutations in the DET2 gene uncouple light signals from a number of light-dependent processes. det2 mutations result in dark-grown Arabidopsis thaliana seedlings with many characteristics of light-grown plants, including hypocotyl growth inhibition, cotyledon expansion, primary leaf initiation, anthocyanin accumulation, and derepression of light-regulated gene expression. In contrast to these morphological and gene expression changes, however, the chloroplast development program is not initiated in the dark in det2 mutants, suggesting that light-regulated gene expression precedes the differentiation of etioplasts to chloroplasts. det2 mutations thus reveal at least two classes of downstream light-regulated responses that differ in their timing and control mechanisms. Homozygous det2 mutations also affect photoperiodic responses in light-grown plants, including timing of flowering, dark adaptation of gene expression, and onset of leaf senescence. The phenotype of det1 det2 double mutants is additive, implying that DET1 and DET2 function in distinct pathways that affect downstream light-regulated genes. Furthermore, these pathways are not utilized solely during early seedling development but must also be required to regulate different aspects of the light developmental program during later stages of vegetative growth.     

A mutation in the Arabidopsis DET3 gene uncouples photoregulated leaf development from gene expression and chloroplast biogenesis

The genetic and phenotypic characterization of a new Arabidopsis mutant, de-etiolated -3, ( det 3), involved in light-regulated seedling development is described. A recessive mutation in the DET 3 gene uncouples light signals from a subset of light-dependent processes. The det 3 mutation causes dark-grown Arabidopsis thaliana seedlings to have short hypocotyls, expanded cotyledons, and differentiated leaves, traits characteristic of light-grown seedlings. Despite these morphological changes, however, the det 3 mutant does not develop chloroplasts or show elevated expression of nuclear- and chloroplast-encoded light-regulated mRNAs. The det 3 mutation thus uncovers a downstream branch of the light transduction pathways that separates leaf development from chloroplast differentiation and light-regulated gene expression. In addition, light-grown det 3 plants have reduced stature and apical dominance, suggesting that DET3 functions during growth in normal light conditions as well. The genetic interactions between mutations in det 1, det 2, and det 3 are described. The phenotypes of doubly mutant strains suggest that there are at least two parallel pathways controlling light-mediated development in Arabidopsis .     

植物光调控因子COP1、HY5的研究进展

植物光形态建成调控因子COP1黑暗中积累在细胞核内,直接与碱性亮氨酸拉链（bZIP）类转录因子HY5相互作用,并被蛋白酶降解,负调控下游基因的表达;而在光下COP1从细胞核内转移到细胞核外,HY5得以在细胞核内积累,可特异结合于查尔酮合成酶基因CHS等光诱导基因启动子上,正调控相关基因的表达。