A GENETIC MODEL FOR LIGHT-REGULATED SEEDLING DEVELOPMENT IN ARABIDOPSIS

The genetic interactions among mutations that define eight distinct loci involved in light-regulated development in Arabidopsis thaliana are described. The mutations in these eight genes define two distinct phenotypic classes with opposite characteristics. Recessive mutation in either one of two genes, DET1 or DET2, result in dark-grown plants that develop as light-grown wild-type seedlings. Mutants in the second class exhibit a reduced response to light. Recessive mutations in any one of five genes, HY1, HY2, HY3, HY5, or HY6 cause reduced responses to red-light. Four of these genes, HY1, 2, 3, and 6, affect the activity of one or all of the red-light photoreceptors, the phytochromes. The HY4 gene product is involved in blue-light perception or action. The experiments described here examine how these eight genes interact to control a particular event, the switch from developmental arrest in the dark (etiolation) to growth in the light (de-etiolation). The phenotypes of doubly mutant strains suggest a hierarchical regulatory network among these genes in the control of the switch from etiolated to de-etiolated growth strategies.