Overexpression of DWARF4 in the brassinosteroid biosynthetic pathway results in increased vegetative growth and seed yield in Arabidopsis

doi:10.1046/j.1365-313x.2001.01055.x

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Wiley InterScience

The Plant Journal

Volume 26 Issue 6, Pages 573 - 582

Published Online: 23 Dec 2001

Published in association with the Society for Experimental Biology

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Overexpression of DWARF4 in the brassinosteroid biosynthetic pathway results in increased vegetative growth and seed yield in Arabidopsis

Sunghwa Choe ¹ , Shozo Fujioka ² , Takahiro Noguchi ³ , Suguru Takatsuto ⁴ , Shigeo Yoshida ² and Kenneth A. Feldmann ^1,5, ^*

¹ Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA, ² RIKEN (The Institute of Physical and Chemical Research), Wako-shi, Saitama 351-0198, Japan, ³ Tama Biochemical Co. Ltd, Shinjuku-ku, Tokyo 163-0704, Japan, ⁴ Department of Chemistry, Joetsu University of Education, Joetsu-shi, Niigata 943-8512, Japan, ⁵ Ceres, Inc., 3007 Malibu Canyon Road, Malibu, California 90265, USA

^* For correspondence (fax +1 310 317 8998; e-mail kfeldmann@ceres-inc.com).

KEYWORDS

brassinolide • cell elongation • CYP90B1 • cytochrome P₄₅₀ • DWARF4 • steroid hormones

ABSTRACT

Summary

Plants unable to synthesize or perceive brassinosteroids (BRs) are dwarfs. Arabidopsis dwf4 was shown to be defective in a steroid 22α hydroxylase (CYP90B1) step that is the putative rate-limiting step in the BR biosynthetic pathway. To better understand the role of DWF4 in BR biosynthesis, transgenic Arabidopsis plants ectopically overexpressing DWF4 (AOD4) were generated, using the cauliflower mosaic virus 35S promoter, and their phenotypes were characterized. The hypocotyl length of both light- and dark-grown AOD4 seedlings was increased dramatically as compared to wild type. At maturity, inflorescence height increased >35% in AOD4 lines and >14% in tobacco DWF4 overexpressing lines (TOD4), relative to controls. The total number of branches and siliques increased more than twofold in AOD4 plants, leading to a 59% increase in the number of seeds produced. Analysis of endogenous BR levels in dwf4, Ws-2 and AOD4 revealed that dwf4 accumulated the precursors of the 22α-hydroxylation steps, whereas overexpression of DWF4 resulted in increased levels of downstream compounds relative to Ws-2, indicative of facilitated metabolic flow through the step. Both the levels of DWF4 transcripts and BR phenotypic effects were progressively increased in dwf4, wild-type and AOD4 plants, respectively. This suggests that it will be possible to control plant growth by engineering DWF4 transcription in plants.