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

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.

A Wheat Cinnamyl Alcohol Dehydrogenase TaCAD12 Contributes to Host Resistance to the Sharp Eyespot Disease

“…Mutations or down-regulation of monolignol biosynthesis-related genes lead to reduction in lignin biosynthesis/concentration (Piquemal et al, 1998; Sibout et al, 2005; Do et al, 2007; Sattler et al, 2009; Tamasloukht et al, 2011; Thévenin et al, 2011; Scully et al, 2016). For example, in sorghum, brown midrib 6 mutants (mutations in the evolutionary conserved amino acids of SbCAD2 ) have been shown to have limited CAD activity and to reduce the abundance of lignin (Sattler et al, 2009; Scully et al, 2016).…”

Nutrient Changes and in Vitro Digestibility in Generative Stage of M10-BMR Sorghum Mutant Lines

“…The low sugar content in the flowering phase was caused by the translocation of photosynthesis materials into the seeds, and a part of the sugar in sorghum stem was used as energy to support plant physiological process (Sucipto, 2010). Low lignin content in BMR mutant lines is caused by the sugar content of the stem was higher than a non-BMR mutant line (Scully et al, 2016).…”

Identification, Characterization, and Expression Analysis of Cell Wall Related Genes in Sorghum bicolor (L.) Moench, a Food, Fodder, and Biofuel Crop

“…In sorghum, several mutants ( bmr, brown midrib , and rg, red for green ) with reduced lignin content showed increase in saccharification and digestibility compared to control plants (Palmer et al, 2008; Xin et al, 2008; Saballos et al, 2009; Yan et al, 2012; Petti et al, 2013; Sattler et al, 2014). Among these bmr mutants, several loci have been identified which includes bmr2 encoding 4-coumarate: coenzyme A ligase (4CL), bmr6 encoding cinnamyl alcohol dehydrogenase (CAD), and bmr12 and bmr18 encoding caffeic acid O-methyltransferase (COMT) enzymes of monolignol pathways (Saballos et al, 2009; Sattler et al, 2009; Scully et al, 2016). The sorghum biomass digestibility and saccharification efficiency can be further improved by targeting various genes involved in lignin biosynthesis coupled with genes that alter the cellulose crystallinity.…”