title: Homogalacturonan synthesis in Arabidopsis thaliana requires a Golgi-localized protein with a putative methyltransferase domain.
abstract: Pectins are a family of complex cell-wall polysaccharides, the biosynthesis of which remains poorly understood. We identified dwarf mutants with reduced cell adhesion at a novel locus, QUASIMODO2 (QUA2). qua2-1 showed a 50% reduction in homogalacturonan (HG) content compared with the wild type, without affecting other cell-wall polysaccharides. The remaining HG in qua2-1 showed an unaltered degree of methylesterification. Positional cloning and GFP fusions showed that QUA2, consistent with a role in HG synthesis, encodes a Golgi-localized protein. In contrast to QUA1, another Golgi-localized protein required for HG-synthesis, QUA2 does not show sequence similarity to glycosyltransferases, but instead contains a putative methyltransferase (MT) domain. The Arabidopsis genome encodes 29 QUA2-related proteins. Interestingly, the transcript profiles of QUA1 and QUA2 are correlated and other pairs of QUA1 and QUA2 homologues with correlated transcript profiles can be identified. Together, the results lead to the hypothesis that QUA2 is a pectin MT, and that polymerization and methylation of homogalacturonan are interdependent reactions.
authors.affiliation: Laboratoire de Biologie Cellulaire, Institut Jean-Pierre Bourgin, INRA, Route de Saint Cyr, 78026 Versailles Cedex, France. gmouille@versailles.inra.fr
authors.forename: Grégory
authors.initials: G
authors.lastname: Mouille
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Ralet
authors.forename: Céline
authors.initials: C
authors.lastname: Cavelier
authors.forename: Cathlene
authors.initials: C
authors.lastname: Eland
authors.forename: Delphine
authors.initials: D
authors.lastname: Effroy
authors.forename: Kian
authors.initials: K
authors.lastname: Hématy
authors.forename: Lesley
authors.initials: L
authors.lastname: McCartney
authors.forename: Hoai Nam
authors.initials: HN
authors.lastname: Truong
authors.forename: Virginie
authors.initials: V
authors.lastname: Gaudon
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Thibault
authors.forename: Alan
authors.initials: A
authors.lastname: Marchant
authors.forename: Herman
authors.initials: H
authors.lastname: Höfte
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000201:enzymology / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D010368:Pectins / Q000096:biosynthesis*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D029681:Arabidopsis Proteins; D049452:Green Fluorescent Proteins; D010368:Pectins; D008780:Methyltransferases; C003181:polygalacturonic acid