title: The transcriptional regulator LEUNIG_HOMOLOG regulates mucilage release from the Arabidopsis testa.
abstract: Exposure of the mature Arabidopsis (Arabidopsis thaliana) seed to water results in the rapid release of pectinaceous mucilage from the outer cells of the testa. Once released, mucilage completely envelops the seed in a gel-like capsule. The physical force required to rupture the outer cell wall of the testa comes from the swelling of the mucilage as it expands rapidly following hydration. In this study, we show that mutations in the transcriptional regulator LEUNIG_HOMOLOG (LUH) cause a mucilage extrusion defect due to altered mucilage swelling. Based on sugar linkage and immunomicroscopic analyses, we show that the structure of luh mucilage is altered, having both an increase in substituted rhamnogalacturonan I and in methyl-esterified homogalacturonan. Also correlated with the structural modification of luh mucilage is a significant decrease in MUCILAGE MODIFIED2 (MUM2; a β-galactosidase) expression in the luh seed coat, raising the possibility that reduced activity of this glycosidase is directly responsible for the luh mucilage defects. Consistent with this is the structural similarity between mum2 and luh mucilage as well as the observation that elevating MUM2 expression in luh mutants completely suppresses the mucilage extrusion defect. Suppression of the luh mutant phenotype was also observed when LEUNIG, a transcriptional corepressor closely related to LUH, was introduced in luh mutants under the control of the LUH promoter. Based on these data, we propose a new model for the regulation of pectin biosynthesis during plant growth and development.
authors.affiliation: Genetics Department , University of Melbourne, Victoria 3010, Australia.
authors.forename: Murray
authors.initials: M
authors.lastname: Walker
authors.forename: Muhammad
authors.initials: M
authors.lastname: Tehseen
authors.forename: Monika S
authors.initials: MS
authors.lastname: Doblin
authors.forename: Filomena A
authors.initials: FA
authors.lastname: Pettolino
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Wilson
authors.forename: Antony
authors.initials: A
authors.lastname: Bacic
authors.forename: John F
authors.initials: JF
authors.lastname: Golz
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D009154:Mutation; D009928:Organ Specificity; D010641:Phenotype; D062087:Plant Mucilage / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D012639:Seeds / Q000201:enzymology* / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C417768:LUG protein, Arabidopsis; C560407:LUH protein, Arabidopsis; D062087:Plant Mucilage; D012097:Repressor Proteins; D014157:Transcription Factors; C000597451:MUM2 protein, Arabidopsis; D001616:beta-Galactosidase