Functional analysis of lignin biosynthetic genes
Lignin is one of main components in plant secondary cell walls. It's most abundant terrestrial biomass on the earth. Though lignin is very important for plant viability, it presents a major obstacle that hinders the utilization of plant biomass as forage and as raw material for pulp and paper production. The biosynthesis of lignin in plants requires enzymes for the synthesis of monolignols and their polymerization. Many genes for lignin biosynthesis, including isogenes that belong to individual gene families, have been cloned and relationships between their expression and the biosynthesis of lignin in the lignifying cells and tissues have been characterized in various plants. Using model plants (tobacco and arabidopsis) and model trees (poplar and aspen), we investigate functions of several genes involved in lignin biosynthesis (4-coumarate:CoA ligase, caffeate/5-hydroxyferulateO-methyltransferase, peroxidase and others).
Molecular mechanisms of secondary cell wall biosynthesis
Xylem tissue with secondary cell wall plays important roles in plants, being involved in water transport, mechanical support and resistance to microorganisms. The differentiation processes of the tissue are one of the most extensively studied aspects of plant development. To clarify the physiological roles of the xylem tissue and the details of the mechanism of xylem differentiation, it is important to establish the details of the formation of the secondary wall in xylem cells during their differentiation. In addition, the molecular aspects of lignification during xylem differentiation are also interest since modifications of the lignin structure and lignin content in xylem tissue should believe to contribute to improvements in the availability of biomass derived from wood. To understand how lignin biosynthesis is regulated during cell and tissue differentiations, we try to isolate novel mutant of model plants (Arabidopsis and poplar) by screening of mutant pools, which constructed by T-DNA tagging and activation tagging procedure. The mutants will be isolated in our future projects should contribute to clarify molecular mechanisms of formation of secondary cell wall and lignification of the xylem tissues.
Biotechnology for phytoremediation by transgenic plants with genes isolated from plants, fungi and bacteria
Extracellular enzymes from white basidiomycetes (laccase, peroxidase and Mn-peroxidase) and bacterial catabolitic enzymes can degrade a various type of phenolic compounds. In addition, some plant and bacteria can absorb and/or assimilate heavy metals from the environment. Transgenic plants with genes from the fungi and bacteria which contribute to accumulation and/or degradation of heavy metals and the phenolics should be useful for cleaning up of soil and water contaminated with various pollutants. We investigate novel gene for phytoremediation and production of transgenic plants with the genes for construction of new phytoremediation systems.
Challenging towards value-added modification of lignins and wall phenolics by genetic engineering
Despite their importance for plant growth and development, lignins are dealt with nuisance and with waste in some of the industrial processes. For a past decade, many efforts had been performed to modify lignin content and compositions in transgenic plants by genetic engineering. Some of the works contribute to supply superior lignocelluloses for conventional markets such as pulp, paper and forage industries. However, these efforts scarcely lead to adding value of lignin itself. In contrast to relative facilities of chemical and fermentative conversions of polysaccharides in lignocelluloses into fibers, alcohols, and polymeric components, conversion of the lignins as functional and valuable materials is not so easy owing to their structural complexity and heterogeneity. Although lignins and their derivatives are used as important raw materials and intermediates for various end-products such as concrete admixtures, animal feed, blended co-polymers, binders, adhesives, and wood and ceramic composites have been developed so far, most of isolated lignins from the lignocelluloses are still burnt as a fuel. Diversion of the lignins into any functional materials requests consumption of substantial fossil fuel as alternative energy sources for the processes. This is a main reason why most part of the lignins are dealt with fuel. However genetic engineering for modification of the lignins and phenolics may contribute, in part at least, to overcome the obstacle to further valorization of lignins. It can be thought that lignin lays a reliable position as feedstock for a variety of chemicals, in particular, as source of oxygenated aromatic compounds. To contribute the production of the value-added lignins and phenolics, now we try to simplify the lignin structure and composition of phenolic compositions in transgnic plants with combination of various types of genes.