title: The maize brown midrib4 (bm4) gene encodes a functional folylpolyglutamate synthase.
abstract: Mutations in the brown midrib4 (bm4) gene affect the accumulation and composition of lignin in maize. Fine-mapping analysis of bm4 narrowed the candidate region to an approximately 105 kb interval on chromosome 9 containing six genes. Only one of these six genes, GRMZM2G393334, showed decreased expression in mutants. At least four of 10 Mu-induced bm4 mutant alleles contain a Mu insertion in the GRMZM2G393334 gene. Based on these results, we concluded that GRMZM2G393334 is the bm4 gene. GRMZM2G393334 encodes a putative folylpolyglutamate synthase (FPGS), which functions in one-carbon (C1) metabolism to polyglutamylate substrates of folate-dependent enzymes. Yeast complementation experiments demonstrated that expression of the maize bm4 gene in FPGS-deficient met7 yeast is able to rescue the yeast mutant phenotype, thus demonstrating that bm4 encodes a functional FPGS. Consistent with earlier studies, bm4 mutants exhibit a modest decrease in lignin concentration and an overall increase in the S:G lignin ratio relative to wild-type. Orthologs of bm4 include at least one paralogous gene in maize and various homologs in other grasses and dicots. Discovery of the gene underlying the bm4 maize phenotype illustrates a role for FPGS in lignin biosynthesis.
authors.affiliation: Department of Agronomy, Iowa State University, 2035 Roy J. Carver Co-Lab, Ames, IA, 50011-3650, USA; College of Agronomy, Northwest Agriculture and Forestry University, #3, Taicheng road, Yangling, Shaanxi, 712100, China.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Sarah
authors.initials: S
authors.lastname: Hill-Skinner
authors.forename: Sanzhen
authors.initials: S
authors.lastname: Liu
authors.forename: Danielle
authors.initials: D
authors.lastname: Beuchle
authors.forename: Ho Man
authors.initials: HM
authors.lastname: Tang
authors.forename: Cheng-Ting
authors.initials: CT
authors.lastname: Yeh
authors.forename: Dan
authors.initials: D
authors.lastname: Nettleton
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Schnable
mesh_terms: D053898:Biosynthetic Pathways; D002874:Chromosome Mapping; D005816:Genetic Complementation Test; D018745:Genome, Plant; D008031:Lignin / Q000096:biosynthesis; D009154:Mutation; D010453:Peptide Synthases / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D017423:Sequence Analysis, RNA; D003313:Zea mays / Q000201:enzymology / Q000235:genetics*
chemical_list: D008031:Lignin; D010453:Peptide Synthases; C023103:folylpolyglutamate synthetase
keywords: Zea mays; brown midrib; folylpolyglutamate synthase; lignin; methylenetetrahydrofolate reductase