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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Mutations in UDP-Glucose:Sterol Glucosyltransferase in Arabidopsis Cause Transparent Testa Phenotype and Suberization Defect in Seeds^{1,[C],[W],[OA]}

Department of Horticulture, University of Kentucky, Lexington, Kentucky 40506 (S.D., M.N.); Max Planck Institute of Molecular Plant Physiology, Science Park Golm, 14476 Potsdam, Germany (W.-R.S., V.B.); Keck Graduate Institute of Applied Life Sciences, Claremont, California 91711 (K.S.); Division of Biology, California Institute of Technology, Pasadena, California 91125 (K.S.); Division of Biology, Kansas State University, Manhattan, Kansas 66506 (K.S.); Lawrence Berkeley National Laboratory, Berkeley, California 94720 (M.A., M.Z.); Membrane Biogenesis Laboratory (UMR 5200), Centre National de la Recherche Scientifique-University of Bordeaux 2, 33076 Bordeaux cedex, France (F.B., Y.L.); Institute for Plant Molecular Biology, Unite Propre de Recherche Centre National de la Recherche Scientifique 2357, 67083 Strasbourg, France (P.B.-N., H.S.); Department of Biology (A.C.) and Global Climate and Energy Project (J.M.), Stanford University, Stanford, California 94305; and Energy Biosciences Institute, University of California, Berkeley, California 94720 (K.H., C.S.)

In higher plants, the most abundant sterol derivatives are steryl glycosides (SGs) and acyl SGs. Arabidopsis (Arabidopsis thaliana) contains two genes, UGT80A2 and UGT80B1, that encode UDP-Glc:sterol glycosyltransferases, enzymes that catalyze the synthesis of SGs. Lines having mutations in UGT80A2, UGT80B1, or both UGT80A2 and UGT8B1 were identified and characterized. The ugt80A2 lines were viable and exhibited relatively minor effects on plant growth. Conversely, ugt80B1 mutants displayed an array of phenotypes that were pronounced in the embryo and seed. Most notable was the finding that ugt80B1 was allelic to transparent testa15 and displayed a transparent testa phenotype and a reduction in seed size. In addition to the role of UGT80B1 in the deposition of flavanoids, a loss of suberization of the seed was apparent in ugt80B1 by the lack of autofluorescence at the hilum region. Moreover, in ugt80B1, scanning and transmission electron microscopy reveals that the outer integument of the seed coat lost the electron-dense cuticle layer at its surface and displayed altered cell morphology. Gas chromatography coupled with mass spectrometry of lipid polyester monomers confirmed a drastic decrease in aliphatic suberin and cutin-like polymers that was associated with an inability to limit tetrazolium salt uptake. The findings suggest a membrane function for SGs and acyl SGs in trafficking of lipid polyester precursors. An ancillary observation was that cellulose biosynthesis was unaffected in the double mutant, inconsistent with a predicted role for SGs in priming cellulose synthesis.

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: Seth DeBolt (sdebo2{at}email.uky.edu).

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

^[W] The online version of this article contains Web-only data.

^[OA] Open access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.140582

^* Corresponding author; e-mail sdebo2{at}email.uky.edu.

Received April 29, 2009; accepted July 20, 2009; published July 29, 2009.