Homogalacturonan synthesis in Arabidopsis thaliana requires a Golgi-localized protein with a putative methyltransferase domain.
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.
Mouille
Grégory
G
Laboratoire de Biologie Cellulaire, Institut Jean-Pierre Bourgin, INRA, Route de Saint Cyr, 78026 Versailles Cedex, France. gmouille@versailles.inra.fr
Ralet
Marie-Christine
MC
Cavelier
Céline
C
Eland
Cathlene
C
Effroy
Delphine
D
Hématy
Kian
K
McCartney
Lesley
L
Truong
Hoai Nam
HN
Gaudon
Virginie
V
Thibault
Jean-François
JF
Marchant
Alan
A
Höfte
Herman
H
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
D029681:Arabidopsis Proteins; D049452:Green Fluorescent Proteins; D010368:Pectins; D008780:Methyltransferases; C003181:polygalacturonic acid