title: Mutations in UDP-Glucose:sterol glucosyltransferase in Arabidopsis cause transparent testa phenotype and suberization defect in seeds.
abstract: 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.
authors.affiliation: Department of Horticulture, University of Kentucky, Lexington, Kentucky 40506, USA. sdebo2@email.uky.edu
authors.forename: Seth
authors.initials: S
authors.lastname: DeBolt
authors.forename: Wolf-Rüdiger
authors.initials: WR
authors.lastname: Scheible
authors.forename: Kathrin
authors.initials: K
authors.lastname: Schrick
authors.forename: Manfred
authors.initials: M
authors.lastname: Auer
authors.forename: Fred
authors.initials: F
authors.lastname: Beisson
authors.forename: Volker
authors.initials: V
authors.lastname: Bischoff
authors.forename: Pierrette
authors.initials: P
authors.lastname: Bouvier-Navé
authors.forename: Andrew
authors.initials: A
authors.lastname: Carroll
authors.forename: Kian
authors.initials: K
authors.lastname: Hematy
authors.forename: Yonghua
authors.initials: Y
authors.lastname: Li
authors.forename: Jennifer
authors.initials: J
authors.lastname: Milne
authors.forename: Meera
authors.initials: M
authors.lastname: Nair
authors.forename: Hubert
authors.initials: H
authors.lastname: Schaller
authors.forename: Marcin
authors.initials: M
authors.lastname: Zemla
authors.forename: Chris
authors.initials: C
authors.lastname: Somerville
mesh_terms: D017360:Arabidopsis / Q000196:embryology / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism; D018548:Cotyledon / Q000033:anatomy & histology / Q000502:physiology; D020869:Gene Expression Profiling; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008055:Lipids; D009154:Mutation; D010641:Phenotype; D011994:Recombinant Proteins; D012639:Seeds / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D013213:Starch / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D008055:Lipids; D011994:Recombinant Proteins; C065875:suberin; D002482:Cellulose; D013213:Starch; D005964:Glucosyltransferases; C577617:UGT80B1 protein, Arabidopsis; C085360:sterol 3-beta-glucosyltransferase