Metabolic reprogramming of lignin biosynthesis in crops

Emergence and evolution of sophisticated chemical scaffolds of lignin polymers providing mechanical support for plant tissues, protecting the plant from pathogen invasion and damaging UV, and enhancing the hydrophobicity of the plant vasculature was of paramount importance to land plant evolution and their adaptation to the local ecosystems. Recruitment of enzymes from primary metabolism and their evolutional modification led to biosynthesis of H and G lignin in early terrestrial plants. Evolutional advantage of S lignin in adaptation to environment was a result of the selective structural alterations of the ring modification enzymes such as ferulate 5-hydroxylase and caffeic acid/5-hydroxyferulic acid O-methyltransferase at later stages of evolution. Lignification consequently transformed phenylpropanoid metabolism into a major sink for carbon in plants estimated to represent as much as 30% of the total biomass produced in the biosphere. Significant progress in plant genomics and in sequencing of the plant species that occupy important positions within the evolutionary history of plants along with functional studies of the families of lignin-specific genes in these plants allowed us in-depth understand how lignin biosynthesis was originated and evolved. Accumulated knoweledge also triggered new strategies for targeted re-programming lignin biosynthesis to improve agricultural and economic values of the crops as the great sugar sources for animal feed and biofuels production. Here we review the current knowledge about different aspects of lignin biosynthesis including its evolution, regulation and targeted modification to improve plant cell wall composition for animal health and for biofuel production.