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J Integr Plant Biol. 2016 Feb;58(2):136-49. doi: 10.1111/jipb.12375. Epub 2015 Oct 9.

Characterization of novel Brown midrib 6 mutations affecting lignin biosynthesis in sorghum.

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Grain, Forage, and Bioenergy Research Unit, USDA-ARS, Lincoln, NE, 68583, USA.
Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, NE, 68583, USA.
Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE, 68583, USA.
Plant Stress and Germplasm Development Unit, USDA-ARS, Lubbock, TX, 79414, USA.
Department of Chemistry, University of Nebraska-Kearney, Kearney, NE, 68849, USA.
Department of Microbiology & Cell Science and UF Genetics Institute, University of Florida, Gainesville, FL, 32610, USA.


The presence of lignin reduces the quality of lignocellulosic biomass for forage materials and feedstock for biofuels. In C4 grasses, the brown midrib phenotype has been linked to mutations to genes in the monolignol biosynthesis pathway. For example, the Bmr6 gene in sorghum (Sorghum bicolor) has been previously shown to encode cinnamyl alcohol dehydrogenase (CAD), which catalyzes the final step of the monolignol biosynthesis pathway. Mutations in this gene have been shown to reduce the abundance of lignin, enhance digestibility, and improve saccharification efficiencies and ethanol yields. Nine sorghum lines harboring five different bmr6 alleles were identified in an EMS-mutagenized TILLING population. DNA sequencing of Bmr6 revealed that the majority of the mutations impacted evolutionarily conserved amino acids while three-dimensional structural modeling predicted that all of these alleles interfered with the enzyme's ability to bind with its NADPH cofactor. All of the new alleles reduced in vitro CAD activity levels and enhanced glucose yields following saccharification. Further, many of these lines were associated with higher reductions in acid detergent lignin compared to lines harboring the previously characterized bmr6-ref allele. These bmr6 lines represent new breeding tools for manipulating biomass composition to enhance forage and feedstock quality.


C4 grass; Cinnamyl alcohol dehydrogenase (CAD); EMS mutagenesis; biofuels; forage

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