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ARS Home » Plains Area » Lincoln, Nebraska » Wheat, Sorghum and Forage Research » Research » Publications at this Location » Publication #345000
Title: Overexpression of the Sorghum bicolor SbCCoAOMT alters cell wall associated hydroxycinnamoyl groups

Author
item Tetreault, Hannah
item Scully, Erin
item Gries, Tammy
item Palmer, Nathan - Nate
item Sattler, Scott
item Funnell-Harris, Deanna
item BAIRD, LISA - University Of San Diego
item SERAVALLI, JAVIER - University Of Nebraska
item Sarath, Gautam
item CLEMENTE, THOMAS - University Of Nebraska

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2018
Publication Date: 10/5/2018
Citation: Tetreault, H.M., Scully, E.D., Gries, T.L., Palmer, N.A., Sattler, S.E., Funnell-Harris, D.L., Baird, L., Seravalli, J., Sarath, G., Clemente, T.E. 2018. Over-expression of the sorghum bicolor SbCCoAOMT alters cell wall associated hydroxycinnamoyl moieties. Plant Physiology. 13(10): e0204153. Available: https://doi.org/10.1371/journal.pone.0204153.
DOI: https://doi.org/10.1371/journal.pone.0204153

Interpretive Summary: In the U.S., sorghum biomass (stalks and leaves) serves as an important forage crop for livestock. In addition, sorghum is being developed as a bioenergy crop. Energy and biofuels are produced from the plant cell walls, which are composed of three main components, cellulose, hemicellulose and lignin. The phenolic cell wall polymer, lignin, makes other cell walls components, cellulose and hemicellulose resistant to breakdown into sugars either in livestock digestive systems or for cellulosic biofuels production. However, lignin contains more energy than cellulose or hemicellulose, which make its increase a goal for fortifying the energy content of biomass. Caffeoyl-CoA 3-O-methyltransferase (CCoAOMT) gene encodes an enzyme involved in the synthesis of lignin. To understand the role of this enzyme in lignin synthesis and its effect on cell wall composition, levels of the CCoAOMT enzyme were highly elevated in sorghum plants using biotechnology. The increased levels of this enzyme led to increased levels of phenolic compounds within cell walls, but lignin levels were not increased in these plants. These changes to cell walls were observable through microscopy and in the total energy of biomass. Collectively, this research provides new perspectives on the role of this enzyme in lignin synthesis, and new ways to change cell wall composition to increase the energy content of biomass. This study demonstrates that cell wall composition can be altered in sorghum without affecting lignin concentration or impacting plant growth and development, which will be useful to improve grasses for bioenergy applications.

Technical Abstract: Sorghum (Sorghum bicolor) is a drought tolerant crop, which is being developed as a bioenergy feedstock. The monolignol biosynthesis pathway is a major focus for altering the abundance and composition of lignin. Caffeoyl coenzyme-A O-methyltransferase (CCoAOMT) is an S-adenosyl methionine (SAM)-dependent O-methyltransferase that methylates caffeoyl-CoA to generate feruloyl-CoA, an intermediate required for the biosynthesis of both G- and S-lignin. SbCCoAOMT was overexpressed to assess the impact of increasing the amount of this enzyme on biomass composition. SbCCoAOMT overexpression increased both soluble and cell wall-bound (esterified) ferulic and sinapic acids, however lignin concentration and its composition (S/G ratio) remained unaffected. This increased deposition of hydroxycinnamic acids in these lines led to an increase in total energy content of the stover. In stalk and leaf midribs, the increased histochemical staining and autofluorescence in the cell walls of the SbCCoAOMT overexpression lines also indicate increased phenolic deposition within cell walls, which is consistent with the chemical analyses of soluble and wall-bound hydroxycinnamic acids. The growth and development of overexpression lines were similar to wild-type plants. Likewise, RNA-seq and metabolite profiling showed that global gene expression and metabolite levels in overexpression lines were also relatively similar to wild-type plants. Our results demonstrate that SbCCoAOMT overexpression significantly altered cell wall composition through increases in cell wall associated hydroxycinnamic acids without altering lignin concentration or affecting plant growth and development.