Suberin: waxy, waterproof chemical in some plant cells, notably cork (in stems) and endodermis cells (in roots). Suberin is an extremely complex and irregular material, like lignin -- with which it shares some similarities. Suberin is composed of two physically separated domains: the aliphatic and phenolic. The phenolic domain is rather lignin-like, but with even greater variability, and built on the same basic unit of a di- or tri-hydroxyphenyl group attached to a three-carbon chain, variously oxidized and integrated with the carbohydrates of the cell walls. Perhaps the most common building block is ferulic acid: formally, 3-(2'-methoxy-3'-hydroxyphenyl)-propenoic acid. Distally, the phenolic domain is attached at points by ester linkages to glycerol. The remaining hydroxyls of the glycerol molecule are ester-linked to some strange-looking C-18 to C-30 lipids. These lipids are substituted at C9-10 with one or two hydroxyls, or even with an epoxide link between the two carbons. Finally the ω- position may be oxidized to a carboxylate (alone or esterized to glycerol) or hydroxyl (alone or esterised to ferulic acid). Variations allow for cross-linkage to other suberin molecules via the 9-10 or ω positions. Image adapted from Bernards (2002).

Suberin is a plant cell wall modification that involves the deposition of both a poly(phenolic) and a poly(aliphatic) domain within the same tissue. As such, the deposition of suberin represents the coordinate regulation of both fatty acid metabolism (giving rise to suberin-specific aliphatic compounds) and phenylpropanoid metabolism (givin rise to suberin-specific phenolic compounds). Over the past decade, we have used chemical analyses to identify target metabolites unique to suberin and biochemical analyses to identify unique steps in their biosynthesis. We are now in a position to clone and characterize the genes that encode the enzymes for these unique biochemical steps. With these genes in hand, we will be able to ask questions about the regulation of suberization and study the mechanism(s) by which disparate pathways converge to make the unique material known as suberin.

In addition, we are interested in the role(s) for which plants use secondary metabolites to interact with other organisms. Recently, we have focused on the role of ginsenosides (e.g., Rb1 at right) in the interaction between ginseng and one of its major pathogens, Pythium irregulare.

Our research group is located on the fourth floor of the North Campus Building, forming part of the Environmental Stress Biology Group. Other members of the ESBG include Dr. Norman Huner, Dr. Denis Maxwell and Dr. Charlie Trick.