UPSC-Seminar

Shinya Kajita
Graduate School of Bio-Applications and System Engineering, Tokyo University of Agriculture and Technology

Title of the seminar:
Genetic engineering of lignin using a bacterial gene

Host: Edouard Pesquet
Room: Lilla hörsalen KB3A9

Lignin is one of the major components of the plant cell wall. It is an aromatic polymer with different types of chemical linkage. The most abundant linkage unit in typical native dicot lignin is the ß-aryl ether (ß–O–4) unit, which accounts for over 50% of all units. The benzylic ß-positions of ß–O–4-units are usually hydroxy-substituted. The ß-keto-ß–O–4 units, with carbonyl groups at the benzylic positions, are also found in natural lignins at very low concentrations. These ß-keto ß–O–4 units can be cleaved under alkaline and/or oxidative conditions more easily and faster than the typical ß–O–4-units with benzylic hydroxyl groups. Thus, increasing the abundance of ß-keto-ß–O–4 units as opposed to the typical ß-hydroxy-ß–O–4 units in the lignin backbone can contribute to a reduction in the cost and energy required for chemical pulping and biomass pretreatment processes in cellulosic ethanol production.

Sphingobium sp. strain SYK-6 , a gram-negative bacterium, can utilize various monomeric and dimeric aromatic compounds that are intermediates in the lignin biosynthetic pathway, such as cinnamic acid, cinnamaldehyde, and ß–O–4 dimers. In our previous studies, we isolated and characterized a lot of genes from the bacterium, which were involved in the degradation of these compounds. One of the genes, ligD, encodes C? dehydrogenase, which catalyzes the first step in the cleavage of the ether bond of ß–O–4 dimers. This enzyme oxidizes the alcohol group at benzyl position of the dimers and oligomers to the carbonyl group. Thus, in the present study, we introduced ligD into the plant genome and attempted to generate transgenic plants whose lignin can be easy to remove from the holocellulose fraction. Recombinant LigD , and transgenic Arabidopsis plants with ligD and their lignins have been characterized by chemical, biochemical, and genetic methods.

Reference: Tsuji et al. Plant Biotech J, 13, 821-832 (2015).