title: MUCILAGE-MODIFIED4 encodes a putative pectin biosynthetic enzyme developmentally regulated by APETALA2, TRANSPARENT TESTA GLABRA1, and GLABRA2 in the Arabidopsis seed coat.
abstract: The Arabidopsis seed coat epidermis undergoes a complex process of differentiation that includes the biosynthesis and secretion of large quantities of pectinaceous mucilage, cytoplasmic rearrangement, and secondary cell wall biosynthesis. Mutations in MUM4 (MUCILAGE-MODIFIED4) lead to a decrease in seed coat mucilage and incomplete cytoplasmic rearrangement. We show that MUM4 encodes a putative NDP-l-rhamnose synthase, an enzyme required for the synthesis of the pectin rhamnogalacturonan I, the major component of Arabidopsis mucilage. This result suggests that the synthesis of monosaccharide substrates is a limiting factor in the biosynthesis of pectinaceous seed coat mucilage. In addition, the reduced cytoplasmic rearrangement observed in the absence of a key enzyme in pectin biosynthesis in mum4 mutants establishes a causal link between mucilage production and cellular morphogenesis. The cellular phenotype seen in mum4 mutants is similar to that of several transcription factors (AP2 [APETALA2], TTG1 [TRANSPARENT TESTA GLABRA1], TTG2 MYB61, and GL2 [GLABRA2]). Expression studies suggest that MUM4 is developmentally regulated in the seed coat by AP2, TTG1, and GL2, whereas TTG2 and MYB61 appear to be regulating mucilage production through alternate pathway(s). Our results provide a framework for the regulation of mucilage production and secretory cell differentiation.
authors.affiliation: Botany Department, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Tamara L
authors.initials: TL
authors.lastname: Western
authors.forename: Diana S
authors.initials: DS
authors.lastname: Young
authors.forename: Gillian H
authors.initials: GH
authors.lastname: Dean
authors.forename: Wei Ling
authors.initials: WL
authors.lastname: Tan
authors.forename: A Lacey
authors.initials: AL
authors.lastname: Samuels
authors.forename: George W
authors.initials: GW
authors.lastname: Haughn
mesh_terms: D000269:Adhesives / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000196:embryology / Q000201:enzymology* / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics; D002454:Cell Differentiation; D003001:Cloning, Molecular; D015870:Gene Expression; D017343:Genes, Plant; D016695:Glycosyltransferases / Q000235:genetics* / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D010368:Pectins / Q000096:biosynthesis*; D010641:Phenotype; D010940:Plant Proteins; D012639:Seeds / Q000166:cytology / Q000201:enzymology; D017386:Sequence Homology, Amino Acid
chemical_list: C499534:APETALA2 protein, Arabidopsis; D000269:Adhesives; D029681:Arabidopsis Proteins; C089991:GL2 protein, Arabidopsis; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D010940:Plant Proteins; C121067:TTG1 protein, Arabidopsis; D010368:Pectins; D016695:Glycosyltransferases