PMID:12756532

Citation	Bout, S and Vermerris, W (2003) A candidate-gene approach to clone the sorghum Brown midrib gene encoding caffeic acid O-methyltransferase. Mol. Genet. Genomics 269:205-14
Abstract	The brown midrib (bmr) mutants of sorghum have brown vascular tissue in the leaves and stem as a result of changes in lignin composition. The bmr mutants were generated via chemical mutagenesis with diethyl sulfate (DES) and resemble the brown midrib (bm) mutants of maize. The maize and sorghum brown midrib mutants are of particular value for the comparison of lignin biosynthesis across different, yet evolutionarily related, species. Although the sorghum brown midrib mutants were first described in 1978, none of the Brown midrib genes have been cloned. We have used a candidate-gene approach to clone the first Brown midrib gene from sorghum. Based on chemical analyses of the allelic mutants bmr12, bmr18 and bmr26, we hypothesized that these mutants had reduced activity of the lignin biosynthetic enzyme caffeic acid O-methyltransferase (COMT). After a northern analysis revealed strongly reduced expression of the COMT gene, the gene was cloned from the mutants and the corresponding wild types using PCR. In all three mutants, point mutations resulting in premature stop codons were identified: bmr12, bmr18 and bmr26 are therefore mutant alleles of the gene encoding COMT. RT-PCR indicated that all three mutants express the mutant allele, but at much lower levels relative to the wild-type controls. Molecular markers were developed for each of the three mutant alleles to facilitate the use of these mutant alleles in genetic studies and breeding programs.
Links	PubMed Online version:10.1007/s00438-003-0824-4
Keywords	Alleles; Blotting, Northern; Cell Wall/metabolism; Cloning, Molecular; Codon, Nonsense; Gas Chromatography-Mass Spectrometry; Genetic Markers; Lignin/genetics; Lignin/metabolism; Methyltransferases/genetics; Molecular Sequence Data; Mutation; Panicum/genetics; Polymerase Chain Reaction; RNA, Messenger/metabolism; Reverse Transcriptase Polymerase Chain Reaction; Sequence Analysis, DNA; Time Factors
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
SORBI:C5YH12		GO:0009809: lignin biosynthetic process	ECO:0000315:		P		Figures 1 & 2 demonstrate the reduced presence of monolignol biosynthetic precursors. Figure 3 shows the reduced expression of the gene. Figure 7 shows CAPS evidence for the presence of premature stop codon.	complete

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