|KOVACS, FRANK - University Of Nebraska|
|VERMERRIS, WILFRED - University Of Florida|
Submitted to: Journal of Integrative Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2015
Publication Date: 2/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62106
Citation: Scully, E.D., Gries, T.L., Funnell-Harris, D.L., Xin, Z., Kovacs, F.A., Vermerris, W., Sattler, S.E. 2016. Characterization of novel Brown midrib 6 mutations affecting lignin biosynthesis in sorghum. Journal of Integrative Plant Biology. 58:136-149. doi:10.1111/jipb.12375.
Interpretive Summary: Lignin is a structural component of plant cell walls that reduces digestibility and impedes the biofuel production from plant materials. Reducing the abundance of lignin in plant cell walls, therefore, would greatly improve digestibility for cattle grazing and increase ethanol production per unit biomass. Brown midrib mutant plants have altered leaf midrib color, more importantly, however, these plants have lower lignin concentrations than normal plants. The Brown midrib 6 (Bmr6) gene of sorghum produces an enzyme that catalyzes the last step in lignin synthesis, and mutations in this gene have been associated with lower lignin levels and increased biofuel yields. In this study, we identified sorghum plants that carry several new mutations in the Bmr6 gene. These mutations significantly disrupted the structure of the Bmr6 protein and led to large reductions in enzyme activity levels. These mutations also led to reductions in lignin content, which may improve conversion of biomass to ethanol. These plants represent new materials that can be used for breeding sorghum with reduce lignin content for bioenergy and grazing purposes.
Technical Abstract: 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.