PMID:19363091

Citation	Sattler, SE, Saathoff, AJ, Haas, EJ, Palmer, NA, Funnell-Harris, DL, Sarath, G and Pedersen, JF (2009) A nonsense mutation in a cinnamyl alcohol dehydrogenase gene is responsible for the Sorghum brown midrib6 phenotype. Plant Physiol. 150:584-95
Abstract	Brown midrib6 (bmr6) affects phenylpropanoid metabolism, resulting in reduced lignin concentrations and altered lignin composition in sorghum (Sorghum bicolor). Recently, bmr6 plants were shown to have limited cinnamyl alcohol dehydrogenase activity (CAD; EC 1.1.1.195), the enzyme that catalyzes the conversion of hydroxycinnamoyl aldehydes (monolignals) to monolignols. A candidate gene approach was taken to identify Bmr6. Two CAD genes (Sb02g024190 and Sb04g005950) were identified in the sorghum genome based on similarity to known CAD genes and through DNA sequencing a nonsense mutation was discovered in Sb04g005950 that results in a truncated protein lacking the NADPH-binding and C-terminal catalytic domains. Immunoblotting confirmed that the Bmr6 protein was absent in protein extracts from bmr6 plants. Phylogenetic analysis indicated that Bmr6 is a member of an evolutionarily conserved group of CAD proteins, which function in lignin biosynthesis. In addition, Bmr6 is distinct from the other CAD-like proteins in sorghum, including SbCAD4 (Sb02g024190). Although both Bmr6 and SbCAD4 are expressed in sorghum internodes, an examination of enzymatic activity of recombinant Bmr6 and SbCAD4 showed that Bmr6 had 1 to 2 orders of magnitude greater activity for monolignol substrates. Modeling of Bmr6 and SbCAD4 protein structures showed differences in the amino acid composition of the active site that could explain the difference in enzyme activity. These differences include His-57, which is unique to Bmr6 and other grass CADs. In summary, Bmr6 encodes the major CAD protein involved in lignin synthesis in sorghum, and the bmr6 mutant is a null allele.
Links	PubMed PMC2689950 Online version:10.1104/pp.109.136408
Keywords	Alcohol Oxidoreductases/chemistry; Alcohol Oxidoreductases/genetics; Alcohol Oxidoreductases/metabolism; Amino Acid Sequence; Base Sequence; Codon, Nonsense/genetics; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Genes, Plant; Immunoblotting; Kinetics; Lignin/metabolism; Molecular Sequence Data; Phenols/metabolism; Phenotype; Phylogeny; Plant Proteins/chemistry; Plant Proteins/genetics; Plant Proteins/metabolism; Plant Stems/enzymology; Plant Stems/genetics; Sequence Alignment; Sorghum/enzymology; Sorghum/genetics; Substrate Specificity
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
SORBI:A1ILL4		GO:0016491: oxidoreductase activity	ECO:0000314:		F		Table 1	complete
SORBI:A1ILL4		GO:0004024: alcohol dehydrogenase activity, zinc-dependent	ECO:0000314:		F		Table 1	complete
SORBI:A1ILL4		GO:0009809: lignin biosynthetic process	ECO:0000315:		P		Figure 2	complete

References

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