The impact of phenylpropanoid pathway manipulation on lignin deposition and soluble secondary metabolism in Arabidopsis
The phenylpropanoid pathway, which is conserved throughout land plants, is responsible for the biosynthesis of many compounds that are involved in plants' structural integrity, water transport, UV protection, and defense against herbivores. The major end product of the phenylpropanoid pathway is lignin, a complex polymer of the secondary cell wall. Decreasing or altering lignin structure provides enhanced cell wall digestibility and can greatly increase the utilization of lignin itself or cell wall polysaccharides. Due to the agro-industrial importance of lignin, the genes participating in lignin biosynthesis have been identified and manipulated in many plant species. Here we describe the metabolic changes that result from the stacking of two manipulation strategies to tailor make high aldehyde lignin. We also show that significant metabolic plasticity is observed in both the soluble and cell wall-bound pools in plants with perturbed lignin biosynthesis. Carbon flux which is normally directed toward one or more metabolites in wild-type plants is instead redirected to another biosynthetically related compound or group of compounds. However, this redirection is not always observed. Here we show a specific example of inhibited plasticity that is most likely the result of transcriptional feedback involving the Mediator complex. In addition to metabolic changes, some perturbations in lignin biosynthesis affect development and can result in dwarfism. These observations may indicate a direct impact of altered lignin and cell wall architecture on plant growth, or it may suggest that lignin biosynthesis is tied to other metabolic networks that affect plant growth and development.
Chapple, Purdue University.
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