First published online May 20, 2005; 10.1104/pp.104.058040
Plant Physiology 138:1117-1125 (2005)
© 2005 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
Brassinosteroid Homeostasis in Arabidopsis Is Ensured by Feedback Expressions of Multiple Genes Involved in Its Metabolism
Kiwamu Tanaka,
Tadao Asami,
Shigeo Yoshida,
Yasushi Nakamura,
Tomoaki Matsuo and
Shigehisa Okamoto*
Department of Agricultural Sciences and Natural Resources (K.T., S.O.), and Department of Biochemical Science and Technology (T.M.), Kagoshima University, Kagoshima 8900065, Japan; Institute of Physical and Chemical Research, Wako, Saitama 3510198, Japan (T.A., S.Y.); and Department of Food Science and Nutritional Health, Kyoto Prefectural University, Sakyo-ku, Kyoto 6068522, Japan (Y.N.)
Homeostasis of brassinosteroids (BRs) is essential for normal growth and development in higher plants. We examined responsiveness of 11 BR metabolic gene expressions to the decrease or increase of endogenous BR contents in Arabidopsis (Arabidopsis thaliana) to expand our knowledge of molecular mechanisms underlying BR homeostasis. Five BR-specific biosynthesis genes (DET2, DWF4, CPD, BR6ox1, and ROT3) and two sterol biosynthesis genes (FK and DWF5) were up-regulated in BR-depleted wild-type plants grown under brassinazole, a BR biosynthesis inhibitor. On the other hand, in BR-excessive wild-type plants that were fed with brassinolide, four BR-specific synthesis genes (DWF4, CPD, BR6ox1, and ROT3) and a sterol synthesis gene (DWF7) were down-regulated and a BR inactivation gene (BAS1) was up-regulated. However, their response to fluctuation of BR levels was highly reduced (DWF4) or nullified (the other eight genes) in a bri1 mutant. Taken together, our results imply that BR homeostasis is maintained through feedback expressions of multiple genes, each of which is involved not only in BR-specific biosynthesis and inactivation, but also in sterol biosynthesis. Our results also indicate that their feedback expressions are under the control of a BRI1-mediated signaling pathway. Moreover, a weak response in the mutant suggests that DWF4 alone is likely to be regulated in other way(s) in addition to BRI1 mediation.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.058040.
* Corresponding author; e-mail okamoto{at}agri.kagoshima-u.ac.jp; fax 81992856014.
Received December 14, 2004;
returned for revision February 15, 2005;
accepted February 15, 2005.
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