Abstract
Phenolic esters have attracted considerable interest due to the potential they offer for peroxidase catalysed cross-linking of cell wall polysaccharides. Particularly, feruloyl residues undergo radical coupling reactions that result in cross-linking (intra-/intermolecular) between polysaccharides, between polysaccharides and lignin and, between polysaccharides and proteins. This review addresses for the first time different studies in which it is established that cross-linking by dehydrodiferulates contributes to maize’s defences to pests and diseases. Dehydrodiferulate cross-links are involved in maize defence mechanisms against insects such as the European, Mediterranean, and tropical corn borers and, storage pest as the maize weevil. In addition, cross-links are also discussed to be involved in genetic resistance of maize to fungus diseases as Gibberella ear and stalk rot. Resistance against insects and fungus attending dehydrodiferulates could go hand in hand. Quantitative trait loci mapping for these cell wall components could be a useful tool for enhancing resistance to pest and diseases in future breeding programs.
Highlights
In the Poaceae family the primary cell wall is built of a skeleton of cellulosic microfibrils embedded in a matrix composed mainly of hemicelluloses and smaller amounts of pectins and glycoproteins [1]
In studies of borer resistance, the content of isomers of dehydrodiferulic acids (DFAs) in corn leaves was highly and negatively correlated across genotypes of maize with field leaf damage caused by European corn borer (ECB) [47]
Dehydrodiferulic acids were found to be significantly correlated to tissue toughness and significant negative correlations were found between DFA and leaf feeding damage by both insects
Summary
In the Poaceae family (grasses and cereals) the primary cell wall is built of a skeleton of cellulosic microfibrils embedded in a matrix composed mainly of hemicelluloses (arabinoxylans, xyloglucan and, in some tissues, mixed-linked glucans) and smaller amounts of pectins and glycoproteins [1]. Grasses have unusually high concentrations of ferulic and p-coumaric acids ester-linked to cell wall polymers (Figure 1) [2]. C4 grasses tend to have higher levels of hydroxycinnamic acids than C3 grasses; as C4, maize and sorghum cell walls can contain up to 4% ferulates (monomers plus dimers) and up to 3% p-coumarate [3,4]. Ferulates are intracellularly esterified to the C5-hydroxyl of -L-arabinose sidechains of xylans and deposited into primary and secondary walls of a variety of grass tissues [10,11,12]. During cell wall deposition and lignification, xylans are cross-linked by peroxidase-mediated coupling of ferulate monomers into a complex array of dimers and trimers and by extensive copolymerization of these ferulates into lignin (Figure 1) [13]
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