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ARS Home » Plains Area » Lincoln, Nebraska » Wheat, Sorghum and Forage Research » Research » Publications at this Location » Publication #247724
Title: Brown Midrib Mutations and Their Importance to the Utilization of Grasses

Author
item Sattler, Scott
item Funnell-Harris, Deanna
item Pedersen, Jeffrey

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2010
Publication Date: 3/5/2010
Citation: Sattler, S.E., Funnell-Harris, D.L., Pedersen, J.F. 2010. Brown Midrib Mutations and Their Importance to the Utilization of Grasses. Plant Science. 178:229-238

Interpretive Summary: Brown midrib mutations were observed in corn over 80 years ago. They have subsequently been discovered or created in sorghum and pearl millet. The characteristic brown coloration of the leaf mid veins has been associated with reduced lignin content and altered lignin composition, traits useful to improve forage digestibility for livestock. In corn, brown midrib is long associated with increased livestock digestibility, but at the cost of significantly reduced forage and grain yields. In sorghum, brown midrib yield reduction was ameliorated through construction of hybrids that maintain reduced lignin content and increased digestibility. Near-isogenic sorghum brown midrib lines and hybrids are dispelling old beliefs that brown midrib mutants are significantly more susceptible to plant pathogens and to lodging than their non-brown midrib counterparts. New chemically mutagenized populations hold promise of providing a more complete set of a non-redundant set of mutant genes involved in lignification of grasses. In addition, early reports indicate brown midrib mutants significantly increase conversion of the lignocellulosic plant tissues to ethanol.

Technical Abstract: Brown midrib mutants have been isolated in maize (Zea mays), sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum) arising through either spontaneous occurrence or chemical mutagenesis. The characteristic brown coloration of the leaf mid veins has been associated with reduced lignin content and altered lignin composition, traits useful to improve forage digestibility for livestock. Brown midrib phenotype has led to identification of two homologous loci in maize (bm1 and bm3) and sorghum (bmr6 and bmr12), which encode cinnamyl alcohol dehydrogenase (CAD) and a caffeic O-methyl transferase (COMT). These enzymes are involved in the last two steps of monolignol biosynthesis. In maize, bm phenotype is long associated with increased livestock digestibility, but at the cost of significantly reduced forage and grain yields. In sorghum, yield reductions were apparent in near isogenic lines, but were ameliorated through construction of hybrids that maintain reduced lignin content and increased digestibility. Near-isogenic sorghum brown midrib lines and hybrids are dispelling old beliefs that brown midrib mutants are significantly more susceptible to plant pathogens and to lodging than their non-brown midrib counterparts. New chemically mutagenized populations hold promise of turning brown midrib phenotype into a non-redundant set of genes involved in lignification of grasses. In addition, early reports indicate brown midrib mutants significantly increase conversion rate in the lignocellulosic bioenergy process.