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DEVELOPMENT AND HORMONE ACTION

A Leaky Mutation in DWARF4 Reveals an Antagonistic Role of Brassinosteroid in the Inhibition of Root Growth by Jasmonate in Arabidopsis^1,[C]

College of Bioscience and Biotechnology, Crop Gene Engineering Key Laboratory of Hunan Province (C.R., C.H., Y.H., Z.P.), College of Horticulture and Landscape (X.X., Q.Z.), and College of Bio-Safety Science and Technology (B.G.), Hunan Agricultural University, Changsha 410128, China; and School of Life Sciences, Tsinghua University, Beijing 100084, China (C.H., W.P., Y.H., D.X.)

The F-box protein CORONATINE INSENSITIVE1 (COI1) plays a central role in jasmonate (JA) signaling and is required for all JA responses in Arabidopsis (Arabidopsis thaliana). To dissect JA signal transduction, we isolated the partially suppressing coi1 (psc1) mutant, which partially suppressed coi1 insensitivity to JA inhibition of root growth. The psc1 mutant partially restored JA sensitivity in coi1-2 background and displayed JA hypersensitivity in wild-type COI1 background. Genetic mapping, sequence analysis, and complementation tests revealed that psc1 is a leaky mutation of DWARF4 (DWF4) that encodes a key enzyme in brassinosteroid (BR) biosynthesis. Physiological analysis showed that an application of exogenous BR eliminated the partial restoration of JA sensitivity by psc1 in coi1-2 background and the JA hypersensitivity of psc1 in wild-type COI1 background. Exogenous BR also attenuated JA inhibition of root growth in the wild type. In addition, the expression of DWF4 was inhibited by JA, and this inhibition was dependent on COI1. These results indicate that (1) BR is involved in JA signaling and negatively regulates JA inhibition of root growth, and (2) the DWF4 is down-regulated by JA and is located downstream of COI1 in the JA-signaling pathway.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Daoxin Xie (daoxinlab{at}tsinghua.edu.cn).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.140202

^* Corresponding author; e-mail daoxinlab{at}tsinghua.edu.cn.

Received April 29, 2009; accepted September 1, 2009; published September 9, 2009.