Submitted to: Phytochemistry Reviews
Publication Type: Review Article
Publication Acceptance Date: 2/10/2010
Publication Date: 3/9/2010
Citation: Hatfield, R.D., Marita, J.M. 2010. Enzymatic Processes Involved in the Incorporation of Hydroxycinnamates into Grass Cell Walls. Phytochemistry Reviews. 9:35-45.
Interpretive Summary: Forages that belong to the grass family play a critical role in providing feedstuffs for animals in the form of fresh herbage (grazing animals) or preserved feed (silage and hay). New use of grasses as feedstocks for the bioenergy industry has increased the demand for plant materials with the highest energy conversion potential as possible. This goal to capture as much of the potential energy stored in plant fibers is the same for dairy production and bioenergy. In dairy production, the end result is more milk/meat with decreased manure waste. For bioenergy, it is to decrease our dependence upon fossil fuels. To accomplish these goals, it is important to understand how the fiber portion (cell walls) of forages is synthesized and how plant developmental changes can alter fiber composition. Once we have acquired this knowledge, we can use it to identify critical features that can be manipulated either through genetic selection or molecular approaches aimed at selective gene manipulation. Two critical structural features of grass cell walls involve the incorporation of the p-coumarates and ferulates into the wall matrix. The incorporation of ferulates and p-coumarates is dependent upon the activity of two specialized enzymes referred to as transferases. Understanding how these enzymes are involved in the formation of ferulate and p-coumarate wall components is critical to developing useful strategies for improving forage utilization. This review highlights recent advances in understanding how these transferases work during plant development. This information will be useful to other scientists who are working on grass cell walls, as well as providing information useful to plant geneticists.
Technical Abstract: Many plant species have one or more types of acylation of cell wall polymers. Grasses (Poaceae family) are unique with abundant acylation of specific cell wall polymers by hydroxycinnamates. The most common hydroxycinnamates found in a wide range of grasses are ferulates (trans-4-hydroxy-3-methoxycinnamic acid) and p-coumarates (trans-4-hydroxycinnamic acid). These two hydroxycinnamates are synthesized by the phenylpropanoid pathway and are structurally related. Though structurally related, they seem to have different functional roles within the cell wall. Ferulates have been shown to have a critical role in cross-linking cell wall components: links between structural polysaccharides and links between structural polysaccharides and lignin. They are distinct in how they are incorporated into the cell wall. Ferulic acid is incorporated into cell walls as ester-linked side chains on arabinoxylans. The exact role p-coumarates play in plant cell walls is unknown, but it has been shown that p-coumaric acid is ester-linked to monolignols and shuttled out to the wall to become incorporated into newly forming lignin polymers. Both processes of incorporation require the activity of specific hydroxycinnamoyl transferases utilizing CoA derivatives to drive the transferase reactions.