Abstract
Homeostasis of brassinosteroids (BRs) is essential for normal growth and development in plants. Herein, we examined responsiveness of 11 BR metabolic genes, which are involved either in sterol biosynthesis, BR specific biosynthesis or BR inactivation, to the decrease or increase of endogenous BRs in wild-type Arabidopsis. Brassinazole, a BR biosynthesis inhibitor, upregulated seven BR biosynthesis genes, FK, DWF5, DET2, DWF4, CPD, BR6ox1, and ROT3. On the other hand, brassinolide downregulated five BR biosynthesis genes, DWF7, DWF4, CPD, BR6ox1, and ROT3, but upregulated a BR inactivation gene, BAS1. Furthermore, these genes responded little (DWF4) or not at all (the other genes) to both chemicals in a bri1 mutant. Taken together, our results suggest that BR homeostasis is maintained through feedback expressions of multiple BR metabolic genes. Moreover, the feedback expressions are under the control of a BRI1-mediated signaling pathway, but DWF4 alone is likely regulated also in other pathway(s).
