Title: Time course field analysis of COMT-downregulated switchgrass: Lignification, recalcitrance, and rust susceptibility

Abstract

Modifying plant cell walls by manipulating lignin biosynthesis can improve biofuel yields from lignocellulosic crops. For example, transgenic switchgrass lines with downregulated expression of caffeic acid O-methyltransferase, a lignin biosynthetic enzyme, produce up to 38% more ethanol than controls. The aim of the present study was to understand cell wall lignification over the second and third growing seasons of COMT-downregulated field-grown switchgrass. COMT gene expression, lignification, and cell wall recalcitrance were assayed for two independent transgenic lines at monthly intervals. Switchgrass rust (Puccinia emaculata) incidence was also tracked across the seasons. Trends in lignification over time differed between the 2 years. In 2012, sampling was initiated in mid-growing season on reproductive-stage plants and there was little variation in the lignin content of all lines (COMT-downregulated and control) over time. COMT-downregulated lines maintained 11-16% less lignin, 33-40% lower S/G (syringyl-to-guaiacyl) ratios, and 15-42% higher sugar release relative to controls for all time points. In 2013, sampling was initiated earlier in the season on elongation-stage plants and the lignin content of all lines steadily increased over time, while sugar release expectedly decreased. S/G ratios increased in non-transgenic control plants as biomass accumulated over the season, while remaining relatively stable across the seasonmore » in the COMT-downregulated lines. Differences in cell wall chemistry between transgenic and non-transgenic lines were not apparent until plants transitioned to reproductive growth in mid-season, after which the cell walls of COMT-downregulated plants exhibited phenotypes consistent with what was observed in 2012. There were no differences in rust damage between transgenics and controls at any time point. Finally, these results provide relevant fundamental insights into the process of lignification in a maturing field-grown biofuel feedstock with downregulated lignin biosynthesis.« less

Authors:

Baxter, Holly L. ^[1]; Mazarei, Mitra ^[1]; Fu, Chunxiang ^[2]; Cheng, Qunkang ^[3]; Turner, Geoffrey B. ^[4]; Sykes, Robert W. ^[4]; Windham, Mark T. ^[3]; Davis, Mark F. ^[4]; Dixon, Richard A. ^[2]; Wang, Zeng -Yu ^[2]; Stewart, Jr., C. Neal ^[1]

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+ Show Author Affiliations

1. Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Samuel Roberts Noble Foundation, Ardmore, OK (United States)
3. Univ. of Tennessee, Knoxville, TN (United States)
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of North Texas, Denton, TX (United States)

Publication Date:

Wed May 18 00:00:00 EDT 2016

Research Org.:

National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1334241

Report Number(s):

NREL/JA-5100-66619
Journal ID: ISSN 1939-1234

Grant/Contract Number:  

AC36-08GO28308

Resource Type:

Accepted Manuscript

Journal Name:

BioEnergy Research

Additional Journal Information:

Journal Volume: 9; Journal Issue: 4; Journal ID: ISSN 1939-1234

Publisher:

Springer

Country of Publication:

United States

Language:

English

Subject:

09 BIOMASS FUELS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; biomass; caffeic acid O-methyltransferase (COMT); lignin; lignocellulosic biofuel; switchgrass