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

(2019) Plant Biotechnology Journal. 17(3). p.594-607
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Abstract
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.
Keywords
Biotechnology, Agronomy and Crop Science, Plant Science

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Chicago
Daly, Paul, Christopher McClellan, Marta Maluk, Helena Oakey, Catherine Lapierre, Robbie Waugh, Jennifer Stephens, et al. 2019. “RNAi-suppression of Barley Caffeic Acid O-methyltransferase Modifies Lignin Despite Redundancy in the Gene Family.” Plant Biotechnology Journal 17 (3): 594–607.
APA
Daly, P., McClellan, C., Maluk, M., Oakey, H., Lapierre, C., Waugh, R., Stephens, J., et al. (2019). RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family. Plant Biotechnology Journal, 17(3), 594–607.
Vancouver
1.
Daly P, McClellan C, Maluk M, Oakey H, Lapierre C, Waugh R, et al. RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family. Plant Biotechnology Journal. Wiley; 2019;17(3):594–607.
MLA
Daly, Paul et al. “RNAi-suppression of Barley Caffeic Acid O-methyltransferase Modifies Lignin Despite Redundancy in the Gene Family.” Plant Biotechnology Journal 17.3 (2019): 594–607. Print.
@article{8599133,
  abstract     = {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 {\texttildelow}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 {\texttildelow}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.},
  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},
  issn         = {1467-7644},
  journal      = {Plant Biotechnology Journal},
  language     = {eng},
  number       = {3},
  pages        = {594--607},
  publisher    = {Wiley},
  title        = {RNAi-suppression of barley caffeic acid O-methyltransferase modifies lignin despite redundancy in the gene family},
  url          = {http://dx.doi.org/10.1111/pbi.13001},
  volume       = {17},
  year         = {2019},
}

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