BAS1:: A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis

The Arabidopsis bas1-D mutation suppresses the long hypocotyl phenotype caused by mutations in the photoreceptor phytochrome B (phyB), The adult phenotype of bas1-D phyB-4 double mutants mimics that of brassinosteroid biosynthetic: and response mutants. bas1-D phyB-4 has reduced levels of brassinosteroids and accumulates 26-hydroxybrassinolide in feeding experiments. The basis for the mutant phenotype is the enhanced expression of a cytochrome P450 (CYP72B1), bas1-D suppresses a phyB-null allele, but not a phyA-null mutation, and partially suppresses a cryptochrome-null mutation. Seedlings with reduced BAS? expression are hyperresponsive to brassinosteroids in a light-dependent manner and display reduced sensitivity to light under a variety of conditions, Thus, BAS1 represents one of the control points between multiple photoreceptor systems and brassinosteroid signal transduction.