Expression of S-Adenosyl Methionine Hydrolase Modifies Lignin in Sorghum
Aymerick Eudes1,2* (email@example.com), Yang Tian1,2, Edward Baidoo1,2, Yu Gao1,2, Hemant Choudhary1,3, John M. Gladden1,3, Blake A. Simmons1,2, Jenny M. Mortimer1,2,4, Henrik Scheller1,2,5, and Jay D. Keasling1,2,5
1Joint BioEnergy Institute; 2Lawrence Berkeley National Laboratory; 3Sandia National Laboratories; 4University of Adelaide; and 5University of California–Berkeley
The vision of Joint Bioenergy Institute (JBEI) is that bioenergy crops can be converted into economically viable, carbon-neutral, biofuels and renewable chemicals currently derived from petroleum, and many other bioproducts that cannot be efficiently produced from petroleum.
Plant biomass represents a large renewable source of fermentable sugars for the synthesis of bioproducts. These sugars are stored as cell wall polymers, mainly cellulose and hemicellulose, and are embedded with lignin, which makes their enzymatic hydrolysis challenging. One of the strategies to reduce cell wall recalcitrance is the modification of lignin content and composition. Lignin is a phenolic polymer of methylated aromatic alcohols and its synthesis in tissues developing secondary cell walls is a significant sink for the consumption of the methyl donor S-adenosylmethionine (AdoMet) due to the involvement of methyltransferases. Researchers previously demonstrated in Arabidopsis that specific expression of S-adenosylmethionine hydrolase (AdoMetase, E.C. 18.104.22.168) in stem tissues reduces AdoMet content and impacts lignin biosynthesis (Eudes et al. 2016). This engineering approach was tested in the bioenergy crop sorghum (Sorghum bicolor L.). AdoMetase was expressed in sorghum lignifying tissues using the promoter of the caffeic acid O-methyltransferase gene. Both AdoMet content and lignin are reduced in transgenics. 2D-HSQC NMR analysis of cell walls showed relative enrichment of non-methylated p-hydroxycinnamyl (H) units and a reduction of tricin (T), guaiacyl (G) and syringyl (S) lignin units in transgenics. Gel permeation chromatography revealed differences in the number average molecular weight (Mn) and weight averaged molecular weight (Mw) of lignin in AdoMetase lines. Quantification of cell wall-bound hydroxycinnamates showed a reduction of ferulate in all transgenic lines. These modifications in engineered sorghum result in a diminution of cell wall recalcitrance since higher yields of glucose and xylose were obtained after enzymatic saccharification of biomass compared to wild type plants. Considering that some transgenic lines display no important diminution of biomass yields, this engineering approach provides a valuable option for the improvement of lignocellulosic biomass feedstock.
Eudes, A., et al. 2016. “Expression of S-adenosylmethionine Hydrolase in Tissues Synthesizing Secondary Cell Walls Alters Specific Methylated Cell Wall Fractions and Improves Biomass Digestibility.” Frontiers in Bioengineering and Biotechnology 4(58). DOI: 10.3389/fbioe.2016.00058.
This work was part of the DOE Joint BioEnergy Institute supported by the U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research, through contract DE-AC02-05CH11231 between Lawrence Berkeley National Laboratory and the U.S. Department of Energy.