Abstract
Brz (brassinazole) was synthesized as the first specific inhibitor of brassinosteroid biosynthesis. Target of Brz220 is the cytochrome P450 enzyme encoded by DWF4. In order to analyze in detail the mechanisms of brassinosteroid signal transduction, we screened for mutants that showed longer hypocotyls than wild type when grown with Brz220 in the dark, and designated bil mutants (Brz-insensitive-long hypocotyl). We identified a semidominant mutant, bil5, from fast neutron-treated lines. Hypocotyl elongation of these plants on Brz medium was at least twice that of the wild type. Adult bil5 plants showed pale green, thin stems, thin leaves and shortened stem length. The pale-green leaves of bil5 were in contrast to the dark-green leaves of brassinosteroid-deficient mutants, and chloroplast gene expression was lower in bil5 than in wild type. We also identified a pale green mutant bpg1 (Brz-insensitive-pale green1) that could not be recovered to high green by Brz in the light.
