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Title: RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family

Caffeic acid O-methyltransferase (COMT), the lignin biosynthesis gene modified in many brown-midrib high-digestibility mutants of maize and sorghum, was targeted for downregulation in the small grain temperate cereal, barley (Hordeum vulgare), to improve straw properties. Phylogenetic and expression analyses identified the barley COMT orthologue(s) expressed in stems, defining a larger gene family than in brachypodium or rice with three COMT genes expressed in lignifying tissues. RNAi significantly reduced stem COMT protein and enzyme activity, and modestly reduced stem lignin content while dramatically changing lignin structure. Lignin syringyl-to-guaiacyl ratio was reduced by ~50%, the 5-hydroxyguaiacyl (5-OH-G) unit incorporated into lignin at 10-–15-fold higher levels than normal, and the amount of p-coumaric acid ester-linked to cell walls was reduced by ~50%. No brown-midrib phenotype was observed in any RNAi line despite significant COMT suppression and altered lignin. The novel COMT gene family structure in barley highlights the dynamic nature of grass genomes. Redundancy in barley COMTs may explain the absence of brown-midrib mutants in barley and wheat. The barley COMT RNAi lines nevertheless have the potential to be exploited for bioenergy applications and as animal feed.
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [1] ;  [6] ;  [7] ;  [7] ;  [7] ;  [6] ; ORCiD logo [1]
  1. Univ. of Dundee at the James Hutton Inst., Dundee (United Kingdom)
  2. Univ. of Dundee at the James Hutton Inst., Dundee (United Kingdom); Univ. of Adelaide, SA (Australia)
  3. Univ. Paris-Saclay, Versaille (France)
  4. Univ. of Dundee at the James Hutton Inst., Dundee (United Kingdom); James Hutton Inst., Dundee (United Kingdom)
  5. James Hutton Inst., Dundee (United Kingdom)
  6. Great Lakes Bioenergy Research Center, Madison, WI (United States); Univ. of Wisconsin, Madison, WI (United States)
  7. VIB Center for Plant Systems Biology, Ghent (Belgium); Ghent Univ. (Belgium)
Publication Date:
Grant/Contract Number:
SC0018409
Type:
Accepted Manuscript
Journal Name:
Plant Biotechnology Journal
Additional Journal Information:
Journal Volume: 17; Journal Issue: 3; Journal ID: ISSN 1467-7644
Publisher:
Society for Experimental Biology; Association of Applied Biology
Research Org:
Great Lakes Bioenergy Research Center, Madison, WI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; caffeic acid O-methyltransferase (COMT), lignin, brown-midrib, barley (Hordeum vulgare), straw, RNAi, biofuels, biorefineries
OSTI Identifier:
1505792

Daly, Paul, McClellan, Christopher, Maluk, Marta, Oakey, Helena, Lapierre, Catherine, Waugh, Robbie, Stephens, Jennifer, Marshall, David, Barakate, Abdellah, Tsuji, Yukiko, Goeminne, Geert, Vanholme, Ruben, Boerjan, Wout, Ralph, John, and Halpin, Claire. RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family. United States: N. p., Web. doi:10.1111/pbi.13001.
Daly, Paul, McClellan, Christopher, Maluk, Marta, Oakey, Helena, Lapierre, Catherine, Waugh, Robbie, Stephens, Jennifer, Marshall, David, Barakate, Abdellah, Tsuji, Yukiko, Goeminne, Geert, Vanholme, Ruben, Boerjan, Wout, Ralph, John, & Halpin, Claire. RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family. United States. doi:10.1111/pbi.13001.
Daly, Paul, McClellan, Christopher, Maluk, Marta, Oakey, Helena, Lapierre, Catherine, Waugh, Robbie, Stephens, Jennifer, Marshall, David, Barakate, Abdellah, Tsuji, Yukiko, Goeminne, Geert, Vanholme, Ruben, Boerjan, Wout, Ralph, John, and Halpin, Claire. 2018. "RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family". United States. doi:10.1111/pbi.13001. https://www.osti.gov/servlets/purl/1505792.
@article{osti_1505792,
title = {RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family},
author = {Daly, Paul and McClellan, Christopher and Maluk, Marta and Oakey, Helena and Lapierre, Catherine and Waugh, Robbie and Stephens, Jennifer and Marshall, David and Barakate, Abdellah and Tsuji, Yukiko and Goeminne, Geert and Vanholme, Ruben and Boerjan, Wout and Ralph, John and Halpin, Claire},
abstractNote = {Caffeic acid O-methyltransferase (COMT), the lignin biosynthesis gene modified in many brown-midrib high-digestibility mutants of maize and sorghum, was targeted for downregulation in the small grain temperate cereal, barley (Hordeum vulgare), to improve straw properties. Phylogenetic and expression analyses identified the barley COMT orthologue(s) expressed in stems, defining a larger gene family than in brachypodium or rice with three COMT genes expressed in lignifying tissues. RNAi significantly reduced stem COMT protein and enzyme activity, and modestly reduced stem lignin content while dramatically changing lignin structure. Lignin syringyl-to-guaiacyl ratio was reduced by ~50%, the 5-hydroxyguaiacyl (5-OH-G) unit incorporated into lignin at 10-–15-fold higher levels than normal, and the amount of p-coumaric acid ester-linked to cell walls was reduced by ~50%. No brown-midrib phenotype was observed in any RNAi line despite significant COMT suppression and altered lignin. The novel COMT gene family structure in barley highlights the dynamic nature of grass genomes. Redundancy in barley COMTs may explain the absence of brown-midrib mutants in barley and wheat. The barley COMT RNAi lines nevertheless have the potential to be exploited for bioenergy applications and as animal feed.},
doi = {10.1111/pbi.13001},
journal = {Plant Biotechnology Journal},
number = 3,
volume = 17,
place = {United States},
year = {2018},
month = {8}
}

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