title: Identification and Characterization of Arabidopsis Seed Coat Mucilage Proteins.
abstract: Plant cell wall proteins are important regulators of cell wall architecture and function. However, because cell wall proteins are difficult to extract and analyze, they are generally poorly understood. Here, we describe the identification and characterization of proteins integral to the Arabidopsis (Arabidopsis thaliana) seed coat mucilage, a specialized layer of the extracellular matrix composed of plant cell wall carbohydrates that is used as a model for cell wall research. The proteins identified in mucilage include those previously identified by genetic analysis, and several mucilage proteins are reduced in mucilage-deficient mutant seeds, suggesting that these proteins are genuinely associated with the mucilage. Arabidopsis mucilage has both nonadherent and adherent layers. Both layers have similar protein profiles except for proteins involved in lipid metabolism, which are present exclusively in the adherent mucilage. The most abundant mucilage proteins include a family of proteins named TESTA ABUNDANT1 (TBA1) to TBA3; a less abundant fourth homolog was named TBA-LIKE (TBAL). TBA and TBAL transcripts and promoter activities were detected in developing seed coats, and their expression requires seed coat differentiation regulators. TBA proteins are secreted to the mucilage pocket during differentiation. Although reverse genetics failed to identify a function for TBAs/TBAL, the TBA promoters are highly expressed and cell type specific and so should be very useful tools for targeting proteins to the seed coat epidermis. Altogether, these results highlight the mucilage proteome as a model for cell walls in general, as it shares similarities with other cell wall proteomes while also containing mucilage-specific features.
authors.affiliation: Department of Botany (A.Y.-L.T., T.K., G.W.H.), Michael Smith Laboratories (A.Y.-L.T., J.R., L.J.F., B.E.E.), and Department of Biochemistry and Molecular Biology (L.J.F.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Allen Yi-Lun
authors.initials: AY
authors.lastname: Tsai
authors.affiliation: Department of Botany (A.Y.-L.T., T.K., G.W.H.), Michael Smith Laboratories (A.Y.-L.T., J.R., L.J.F., B.E.E.), and Department of Biochemistry and Molecular Biology (L.J.F.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kunieda
authors.affiliation: Department of Botany (A.Y.-L.T., T.K., G.W.H.), Michael Smith Laboratories (A.Y.-L.T., J.R., L.J.F., B.E.E.), and Department of Biochemistry and Molecular Biology (L.J.F.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Jason
authors.initials: J
authors.lastname: Rogalski
authors.affiliation: Department of Botany (A.Y.-L.T., T.K., G.W.H.), Michael Smith Laboratories (A.Y.-L.T., J.R., L.J.F., B.E.E.), and Department of Biochemistry and Molecular Biology (L.J.F.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Leonard J
authors.initials: LJ
authors.lastname: Foster
authors.affiliation: Department of Botany (A.Y.-L.T., T.K., G.W.H.), Michael Smith Laboratories (A.Y.-L.T., J.R., L.J.F., B.E.E.), and Department of Biochemistry and Molecular Biology (L.J.F.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Ellis
authors.affiliation: Department of Botany (A.Y.-L.T., T.K., G.W.H.), Michael Smith Laboratories (A.Y.-L.T., J.R., L.J.F., B.E.E.), and Department of Biochemistry and Molecular Biology (L.J.F.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 george.haughn@ubc.ca.
authors.forename: George W
authors.identifier: 0000-0001-8164-8826
authors.initials: GW
authors.lastname: Haughn
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D019441:Plant Epidermis / Q000378:metabolism; D062087:Plant Mucilage / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D062087:Plant Mucilage; D012333:RNA, Messenger