A new technology for structural modification of lignin polymer in plants

Lignin is a complex polymer with phenylpropanoid units linked together by various carbon-oxygen and carbon-carbon bonds. It is deposited in plant walls and plays important roles in mechanical support, water transport and stress responses. Although lignin is essential for plant growth and development, it negatively affects the use of lignocellulosic biomass. In many cases, lignin has to be removed to isolate cellulosic and non-cellulosic polysaccharides and this process requires a great deal of energy and chemicals. In order to reduce the lignin recalcitrance through a modification of lignin structure, we introduced ligD gene into a model plant, Arabidopsis thaliana. This gene encodes the polypeptide that can oxidize the benzylic carbon in β–O–4-linked dimers and oligomers of lignin. This oxidation of lignin increases degradability of the polymer in alkaline and acidic conditions. Analysis by nuclear magnetic resonance revealed a 2.1- to 2.8-fold increased level of the oxidized lignin units in the transgenic Arabidopsis plants, indicating that the transformation was capable of altering lignin structure in the desired manner.