Article

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

ABSTRACT

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 2.1.1.6), 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., 2006Fornalé et al., , 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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    ABSTRACT: Lignin is an essential polymer in vascular plants that plays key structural roles in vessels and fibers. Lignification is induced by external inputs such as wounding, but the molecular mechanisms that link this stress to lignification remain largely unknown. In this work, we provide evidence that three maize (Zea mays) lignin repressors, MYB11, MYB31, and MYB42, participate in wound-induced lignification by interacting with ZML2, a protein belonging to the TIFY family. We determined that the three R2R3-MYB factors and ZML2 bind in vivo to AC-rich and GAT(A/C) cis-elements, respectively, present in a set of lignin genes. In particular, we show that MYB11 and ZML2 bind simultaneously to the AC-rich and GAT(A/C) cis-elements present in the promoter of the caffeic acid O-methyl transferase (comt) gene. We show that, like the R2R3-MYB factors, ZML2 also acts as a transcriptional repressor. We found that upon wounding and methyl jasmonate treatments, MYB11 and ZML2 proteins are degraded and comt transcription is induced. Based on these results, we propose a molecular regulatory mechanism involving a MYB/ZML complex in which wound-induced lignification can be achieved by the derepression of a set of lignin genes.
    Full-text · Article · Nov 2015 · The Plant Cell
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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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    ABSTRACT: Indirect plant-mediated interactions between herbivores are important drivers of community composition in terrestrial ecosystems. Among the most striking examples are the strong indirect interactions between spatially separated leaf and root feeding insects sharing a host plant. Although leaf-feeders generally reduce the performance of root herbivores, little is known about the underlying systemic changes in root physiology and the associated behavioral responses of the root feeders. We investigated the consequences of maize leaf-infestation by Spodoptera littoralis caterpillars for the root-feeding larvae of the beetle Diabrotica virgifera, a major pest of maize. Diabrotica virgifera strongly avoided leaf-infested plants by recognizing systemic changes in soluble root components. The avoidance response occurred within 12 hours and was induced by real and mimicked herbivory, but not wounding alone. Roots of leaf-infested plants showed altered patterns in soluble free and soluble conjugated phenolic acids. Biochemical inhibition and genetic manipulation of phenolic acid biosynthesis led to a complete disappearance of the avoidance response of D. virgifera. Furthermore, bioactivity guided fractionation revealed a direct link between the avoidance response of D. virgifera and changes in soluble conjugated phenolic acids in the roots of leaf-attacked plants. Our study provides a physiological mechanism for a behavioral pattern which explains the negative effect of leaf-attack on a root feeding insect. Furthermore, it opens up the possibility to control D. virgifera in the field by genetically mimicking leaf-herbivore induced changes in root phenylpropanoid patterns.
    Full-text · Article · Oct 2015 · Plant physiology
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    • "The sorghum genes encoding the loci bmr19 and bmr29 to bmr32 have not been identified (Saballos et al 2008; Sattler et al 2014). In maize, Bm1, Bm2 and Bm3 have been cloned, and Bm1 and Bm3 encode orthologous genes to Bmr6 and Bmr12, respectively (Vignols et al 1995; Chen et al 2012). The maize Bm2 and Bm4 genes were shown to encode a 1 5 methylenetetrahydrofolate reductase and a folylpolyglutamate synthase respectively, which are involved in S-adenosyl-l-methionine (SAM) biosynthesis (Tang et al 2014; Li et al 2015). "
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    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. This article is protected by copyright. All rights reserved.
    Preview · Article · Jul 2015 · Journal of Integrative Plant Biology
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