Lignins and Lignification

As ever more component monomers are discovered, lignin can no longer be regarded as deriving from just the three canonical monolignols. Pathway intermediates such as the hydroxycinnamaldehydes and their derived hydroxybenzaldehydes, and additional products of truncated biosynthesis such as caffeyl and 5-hydroxyconiferyl alcohols, are now established lignin monomers. The array of acylated monolignols continues to expand with evidence for monolignol benzoates, vanillates, and ferulates that complement the accepted monolignol acetates, p -hydroxybenzoates, and p -coumarates. Game-changing findings have demonstrated that phenolics from alternative pathways, including flavonoids and hydroxystilbenes, are also involved in lignification, expanding the traditional concept. Beyond the basic science intrigue, these findings propound exciting new avenues for valorizing lignins, or for producing more readily extractable/depolymerizable lignins, in crop and bioenergy plants. Delineating the components that plants are already conscripting for lignification and detailing new components they may be induced to utilize are stimulating current research in this area.