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ARS Home » Plains Area » Lincoln, Nebraska » Wheat, Sorghum and Forage Research » Research » Publications at this Location » Publication #329483
Title: Determination of the structure and catalytic mechanism of sorghum bicolor caffeoyl-CoA O-methyltransferase

Author
item WALKER, ALEXANDER - Washington State University
item SATTLER, STEVEN - Washington State University
item RALPH, JOHN - University Of Wisconsin
item VERMERRIS, WILFRED - University Of Florida
item Sattler, Scott
item KANG, CHULHEE - Washington State University
item REGNER, MATT - University Of Washington
item JONES, JEFFREY - Washington State University

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2016
Publication Date: 9/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63168
Citation: Walker, A.M., Sattler, S.A., Ralph, J., Vermerris, W., Sattler, S.E., Kang, C., Regner, M., Jones, J.P. 2016. Determination of the structure and catalytic mechanism of sorghum bicolor caffeoyl-CoA O-methyltransferase. Plant Physiology. 172(1):78-92.

Interpretive Summary: In the US, sorghum biomass (stalks and leaves) serves as an important forage crop for livestock. In addition, sorghum is being developed as a bioenergy crop. Cellulosic biofuels are derived from the breakdown of cell wall polymers (cellulose and hemicellulose) of the biomass to sugars and the conversion of these sugars to fuel molecules. A third cell wall polymer, lignin, makes cell walls resistant to breakdown either in livestock digestive systems or in the cellulosic conversion process. The Caffeoyl-CoA 3-O-methyltransferase (CCoAOMT) gene encodes an enzyme involved in the synthesis of lignin. In order to better understand the function of this unique class of enzymes from sorghum and other grasses, the structure of sorghum CCoAOMT enzyme was characterized to determine how this enzyme synthesizes the chemical compounds required to make lignin. Mutations in the CCoAOMT gene were created to demonstrate the key parts of the enzyme involved in the chemical reaction. Collectively, this research gives a new perspective on how this enzyme functions in lignin synthesis and provides a basis for how similar enzymes interact with a group of compounds analogous to those involved in lignin synthesis. This study potentially provides new strategies for altering cell wall composition in sorghum, which will be useful to improve sorghum and other grasses for bioenergy.

Technical Abstract: Although cold acclimation is a key process in plants from temperate climates, the mechanisms sensing low temperature remain obscure. Here, we show that the accumulation of the organic acid fumaric acid, mediated by the cytosolic fumarase FUM2, is essential for cold acclimation of metabolism in the cold-tolerant model species Arabidopsis (Arabidopsis thaliana). A nontargeted metabolomic approach, using gas chromatography-mass spectrometry, identifies fumarate as a key component of the cold response in this species. Plants of T-DNA insertion mutants, lacking FUM2, show marked differences in their response to cold, with contrasting responses both in terms of metabolite concentrations and gene expression. The fum2 plants accumulated higher concentrations of phosphorylated sugar intermediates and of starch and malate. Transcripts for proteins involved in photosynthesis were markedly down-regulated in fum2.2 but not in wild-type Columbia-0. Plants of fum2 show a complete loss of the ability to acclimate photosynthesis to low temperature. We conclude that fumarate accumulation plays an essential role in low temperature sensing in Arabidopsis, either indirectly modulating metabolic or redox signals or possibly being itself directly involved in cold sensing.