Suberin, a polyester polymer in the cell wall of terrestrial plants, controls the transport of water and nutrients and protects plant from pathogenic infections and environmental stresses. Structurally, suberin consists of aliphatic and aromatic domains; p-hydroxycinnamates, such as ferulate, p-coumarate, and/or sinapate, are the major phenolic constituents of the latter. By analyzing the ''wallbound'' phenolics of mutant lines of Arabidopsis deficient in a family of acyl-CoA dependent acyltransferase (BAHD) genes, we discovered that the formation of aromatic suberin in Arabidopsis, primarily in seed and root tissues, depends on a member of the BAHD superfamily of enzymes encoded by At5g41040. This enzyme exhibits anhydroxyacid hydroxycinnamoyltransferase activity with an in vitro kinetic preference for feruloyl-CoA and 16-hydroxypalmitic acid. Knocking down or knocking out the At5g41040 gene in Arabidopsis reduces specifically the quantity of ferulate in suberin, but does not affect the accumulation of p-coumarate or sinapate. The loss of the suberin phenolic differentially affects the aliphatic monomer loads and alters the permeability and sensitivity of seeds and roots to salt stress. This highlights the importance of suberin aromatics in the polymer's function.BAHD superfamily ͉ wall-bound phenolics L and plants have evolved different mechanical/defensive machineries to reinforce their cell wall integrity and rigidity to protect themselves from various environmental stresses (1). Along with well recognized lignification, cell wall suberization is another physiologically important strategy to regulate the apoplastic transport of water and solutes and to protect the plant from the invasion of pathogens (1-3).Suberin occurs in the cell walls of external and internal plant tissues. Suberized cells primarily are present in underground tissues (e.g., epidermis, endodermis, exodermis, root and tube phellem), in the coats of mature seeds, in the bundle-sheath cells, and in the phellem of aerial tissues that undergo secondary thickening (2, 4).Structurally, suberin is a complex lipophilic polymer, containing a fatty acid-derived domain (aliphatic suberin) and a (poly)hydroxycinnamate domain (aromatic suberin). The aliphatic suberin is a 3D, glycerol-bridged polyester network, comprised primarily of -hydroxyacids and ␣, -dicarboxylic acids, with chain lengths ranging from C-16 to C-32 (mainly C-18). They exist as discrete components between the plasmalemma and the primary cell wall matrix (2, 3, 5). The aromatic domain is principally composed of p-hydroxycinnamates (e.g., ferulate, p-coumarate, and sinapate) and their derivatives and possibly a low level of monolignols (4, 6). The abundance of those phenolics detected in the suberized tissues varies in different species and ranges as high as approximately 10% of total suberin content (3). The aromatic units of suberin are covalently linked with the aliphatic domain through ester bonds. These aromatic units are then presumably polymerized via radical coupling reactions...