Plant Signaling & Behavior 5:8, 1-6; August 2010; © 2010 Landes Bioscience
Unraveling ferulate role in suberin and periderm biology by reverse genetics Olga Serra,1 Mercè Figueras,1 Rochus Franke,2 Salome Prat3 and Marisa Molinas1,* 1
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Laboratori del Suro; Departament de Biologia; Facultat de Ciències; Universitat de Girona; Girona, Spain; 2Institute of Cellular and Molecular Botany; University of Bonn; Bonn, Germany; 3Centro Nacional de Biotecnología; Consejo Superior de Investigaciones Científicas; Campus Universidad Autónoma de Madrid; Madrid, Spain
Key words: BAHD feruloyl acyltransferases, ferulate, periderm, potato tuber skin, suberin, suberized tissues, wax Abbreviations: TEM, transmission electron microscope; SEM, scanning electron microscope; FHT, ω-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase; GPAT5, glycerol phosphate acyltransferase 5 and to restrict infection. Suberization takes place on the periderm of stems, roots and tubers and in a variety of other barrier layers, such as the root endodermis or the seed coat. Suberin is a complex biopolymer made of cross-linked poly(aliphatic) and poly(aromatic) domains (reviewed in refs. 1–5). The aliphatic domain (aliphatic suberin) consists of a glycerol-based fatty acid derived polyester that, on trans-esterification, releases small amounts of p-hydroxycinnamic acid (mainly ferulic) together with aliphatic monomers and glycerol.6 The aromatic domain is a lignin-like polymer of oxydatively cross-linked phenolics.7 Generally, but not always, suberin contains a certain amount of soluble lipids or waxes embedded into the aliphatic polymer matrix.8,9 Suberin and embedded wax are deposited within the primary cell wall to form a secondary wall that usually appears as a lamellar structure of alternating electron-dense (opaque) and electron-translucent (light) bands under the transmission electron microscope (TEM).10 Current models describing the macromolecular structure of suberin assume that the light lamellae correspond to the fatty acid polyester (aliphatic suberin) and the dense lamellae to the aromatics.1,3 These models held that ferulic acid cross-links the aliphatic suberin with aromatics, as it may form carboxyl-ester bonds with aliphatic monomers and non-ester radical coupled bonds with phenolics. This is in agreement with partial depolymerization studies found to yield feruloyl esters of ω-hydroxyacids and primary alcohols and a small quantity of a monoferuloylglycerol.11 It is well known that ferulic acid is an important component to enhance rigidity and strength in grass cell walls,12,13 but also in dicots14 and gymnosperms.15 In these cell walls, ferulic acid is linked to glycans by ester bonds and serves as an initiation site for lignification, acting as a system for cross-linking polysaccharides and lignins.16,17 The role of ferulic acid in suberized cell walls is, however, poorly understood and its function in cross-linking the suberin aliphatic and aromatic domains has not been demonstrated, the macromolecular structure of suberin therefore remaining still ill defined.5 Reverse genetics approaches allowed to demonstrate the role of a number of key genes in the biosynthetic pathway of aliphatic suberin, specifically fatty acid elongases,18,19 ω-hydroxylases20-22 and a glycerol acyltransferase.21,23 Knowledge on aromatic suberin is, however, much more incomplete. Recently, the analysis of Arabidopsis knockout mutants proved the involvement of a
Plant cell walls are dramatically affected by suberin deposition, becoming an impermeable barrier to water and pathogens. Suberin is a complex layered heteropolymer that comprises both a poly(aliphatic) and a poly(aromatic) lignin-like domain. Current structural models for suberin attribute the crosslinking of...
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