The Brown Midrib3 (Bm3) Mutation in Maize Occurs in the Gene Encoding Caffeic Acid O-Methyltransferase

Departament de Genètica Molecular, Centro de Investigación y Desarrollo, Barcelona, Spain.
The Plant Cell (Impact Factor: 9.34). 05/1995; 7(4):407-16. DOI: 10.1105/tpc.7.4.407
Source: PubMed


The brown midrib mutations are among the earliest described in maize. Plants containing a brown midrib mutation exhibit a reddish brown pigmentation of the leaf midrib starting when there are four to six leaves. These mutations are known to alter lignin composition and digestibility of plants and therefore constitute prime candidates in the breeding of silage maize. Here, we show that two independent brown midrib3 (bm3) mutations have resulted from structural changes in the COMT gene, which encodes the enzyme O-methyltransferase (COMT; EC, involved in lignin biosynthesis. Our results indicate that the bm3-1 allele (the reference mutant allele) has arisen from an insertional event producing a COMT mRNA altered in both size and amount. By sequencing a COMT cDNA clone obtained from bm3-1 maize, a retrotransposon with homology to the B5 element has been found to be inserted near the junction of the 3' coding region of the COMT gene intron. The second bm3 allele, bm3-2, has resulted from a deletion of part of the COMT gene. These alterations of the COMT gene were confirmed by DNA gel blot and polymerase chain reaction amplification analyses. These results clearly demonstrate that mutations at the COMT gene give a brown midrib3 phenotype. Thus, the gene genetically recognized as bm3 is the same as the one coding for COMT.

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    • "Despite their different roles in lignin regulation, both factors repress the maize caffeic acid O-methyl transferase (comt) gene (AC196475). Mutations in this gene have been shown to produce the brown midrib3 phenotype (Vignols et al., 1995; Fornalé et al., 2006, 2010). The expression of maize comt is induced by wounding (Capellades et al., 1996) through a mechanism that remains unknown, while it has been demonstrated that the wound induction of the Arabidopsis thaliana COMT is CORONATINE- INSENSITIVE PROTEIN1 COI1 dependent (Reymond et al., 2000). "
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    The Plant Cell 11/2015; DOI:10.1105/tpc.15.00545 · 9.34 Impact Factor
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    • "Bm1 is defective in cinnamyl alcohol dehydrogenase (CAD) activity required to 175 convert phenolic aldehydes into their alcoholic forms (Halpin et al., 1998). The bm3 mutant has a 176 defective caffeic acid O-methyl transferase (COMT), which is necessary for the production of sinapic 177 acid type phenolics and lignin (Vignols et al., 1995). Both mutations exert feedback effects on 178 phenylpropanoid biosynthesis (Guillaumie et al., 2007). "
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    • "The brown midrib mutants have been used to identify and characterize the genes that encode the major enzymes for specific steps of monolignol biosynthesis for C4 grasses (Figure 1). The maize Bm3 and sorghum Bmr12 genes both encode orthologous caffeic acid Omethyltransferase (COMT), which catalyzes the penultimate step in monolignol biosynthesis (Vignols et al. 1995; Bout and Vermerris 2003). The maize Bm1 and the sorghum Bmr6 genes both encode orthologous cinnamyl alcohol dehydrogenase (CAD) (Saballos et al. 2009; Sattler et al. 2009; Chen et al. 2012), which catalyzes the last step in monolignol biosynthesis. "
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