Abstract
Brassinosteroids (BRs) are steroidal phytohormone playing essential roles in growth and development. Two BR-biosynthetic genes, DWF4 and CPD have been reported to be up-regulated in BR deficient mutants, indicating that an endogenous level of BRs is finely controlled by the feedback mechanism. To determine whether other BR-related genes are under the similar control, we examined the expression of these genes in Arabidopsis that was treated with brassinazole (Brz), a BR biosynthesis inhibitor. Among eleven genes we analyzed using quantitative RT-PCR, 7 genes including DWF4 and CPD were up-regulated in their expression by the Brz treatment. Expression of FK and DWF5 were also increased, both of which function in the sterol biosynthesis to provide the precursor compounds of BRs. Altogether, our results suggest that depletion of BR levels in plant cells is compensated by activation of several genes in the sterol biosynthesis as well as the BR biosynthesis.
