Plant Physiology Preview Published on July 22, 2005; 10.1104/pp.105.061598
Received February 17, 2005
Returned for revision May 10, 2005
Accepted May 10, 2005
Arabidopsis cyp51 Mutant Shows Postembryonic Seedling Lethality Associated with Lack of Membrane Integrity
Ho Bang Kim *, Hubert Schaller , Chang-Hyo Goh , Mi Kwon , Sunghwa Choe , Chung Sun An , Francis Durst , Kenneth A. Feldmann , and René Feyereisen
Department of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea
Institut de Biologie Moléculaire des Plantes/Centre National de la Recherche Scientifique, Unité Propre de Recherche 2357, Strasbourg cedex, F-67083, France
Environmental Biotechnology Research Center, Gyeongsang National University, Chinju 660-701, Korea
Ceres, Inc., Thousand Oaks, California 91320
Institut National de la Recherche Agronomique, Centre de Recherches de Sophia Antipolis, Unité Mixte de Recherche 1112, 06903 Sophia Antipolis, France
* Corresponding author; email: hobang{at}snu.ac.kr.
CYP51 exists in all organisms that synthesize sterols de novo. Plant CYP51 encodes an obtusifoliol 14 -demethylase involved in the postsqualene sterol biosynthetic pathway. According to the current gene annotation, the Arabidopsis (Arabidopsis thaliana) genome contains two putative CYP51 genes, CYP51A1 and CYP51A2. Our studies revealed that CYP51A1 should be considered an expressed pseudogene. To study the functional importance of the CYP51A2 gene in plant growth and development, we isolated T-DNA knockout alleles for CYP51A2. Loss-of-function mutants for CYP51A2 showed multiple defects, such as stunted hypocotyls, short roots, reduced cell elongation, and seedling lethality. In contrast to other sterol mutants, such as fk/hydra2 and hydra1, the cyp51A2 mutant has only minor defects in early embryogenesis. Measurements of endogenous sterol levels in the cyp51A2 mutant revealed that it accumulates obtusifoliol, the substrate of CYP51, and a high proportion of 14 -methyl- 8-sterols, at the expense of campesterol and sitosterol. The cyp51A2 mutants have defects in membrane integrity and hypocotyl elongation. The defect in hypocotyl elongation was not rescued by the exogenous application of brassinolide, although the brassinosteroid-signaling cascade is apparently not affected in the mutants. Developmental defects in the cyp51A2 mutant were completely rescued by the ectopic expression of CYP51A2. Taken together, our results demonstrate that the Arabidopsis CYP51A2 gene encodes a functional obtusifoliol 14 -demethylase enzyme and plays an essential role in controlling plant growth and development by a sterol-specific pathway.
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