title: Prolonged expression of the BX1 signature enzyme is associated with a recombination hotspot in the benzoxazinoid gene cluster in Zea mays.
abstract: Benzoxazinoids represent preformed protective and allelopathic compounds. The main benzoxazinoid in maize (Zea mays L.) is 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA). DIMBOA confers resistance to herbivores and microbes. Protective concentrations are found predominantly in young plantlets. We made use of the genetic diversity present in the maize nested association mapping (NAM) panel to identify lines with significant benzoxazinoid concentrations at later developmental stages. At 24 d after imbibition (dai), only three lines, including Mo17, showed effective DIMBOA concentrations of 1.5mM or more; B73, by contrast, had low a DIMBOA content. Mapping studies based on Mo17 and B73 were performed to reveal mechanisms that influence the DIMBOA level in 24 dai plants. A major quantitative trait locus mapped to the Bx gene cluster located on the short arm of chromosome 4, which encodes the DIMBOA biosynthetic genes. Mo17 was distinguished from all other NAM lines by high transcriptional expression of the Bx1 gene at later developmental stages. Bx1 encodes the signature enzyme of the pathway. In Mo17×B73 hybrids at 24 dai, only the Mo17 Bx1 allele transcript was detected. A 3.9kb cis-element, termed DICE (distal cis-element), that is located in the Bx gene cluster approximately 140 kb upstream of Bx1, was required for high Bx1 transcript levels during later developmental stages in Mo17. The DICE region was a hotspot of meiotic recombination. Genetic analysis revealed that high 24 dai DIMBOA concentrations were not strictly dependent on high Bx1 transcript levels. However, constitutive expression of Bx1 in transgenics increased DIMBOA levels at 24 dai, corroborating a correlation between DIMBOA content and Bx1 transcription.
authors.affiliation: Lehrstuhl für Genetik, Wissenschaftszentrum Weihenstephan, Technische Universität München, 85354 Freising, Germany.
authors.forename: Linlin
authors.initials: L
authors.lastname: Zheng
authors.affiliation: USDA ARS, University of Missouri, Columbia, MO 65211, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: McMullen
authors.affiliation: Lehrstuhl für Pflanzenzüchtung, Wissenschaftszentrum Weihenstephan, Technische Universität München, 85354 Freising, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Bauer
authors.affiliation: Lehrstuhl für Pflanzenzüchtung, Wissenschaftszentrum Weihenstephan, Technische Universität München, 85354 Freising, Germany.
authors.forename: Chris-Carolin
authors.initials: CC
authors.lastname: Schön
authors.affiliation: Lehrstuhl für Genetik, Wissenschaftszentrum Weihenstephan, Technische Universität München, 85354 Freising, Germany.
authors.forename: Alfons
authors.initials: A
authors.lastname: Gierl
authors.affiliation: Lehrstuhl für Genetik, Wissenschaftszentrum Weihenstephan, Technische Universität München, 85354 Freising, Germany Monika.Frey@wzw.tum.de.
authors.forename: Monika
authors.initials: M
authors.lastname: Frey
mesh_terms: D000483:Alleles; D020029:Base Pairing / Q000235:genetics; D048588:Benzoxazines / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics; D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics; D003433:Crosses, Genetic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005838:Genotype; D007178:Inbreeding; D005810:Multigene Family; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D040641:Quantitative Trait Loci; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D036226:Seedlings / Q000378:metabolism; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics* / Q000254:growth & development*
chemical_list: D048588:Benzoxazines; D010940:Plant Proteins; D012333:RNA, Messenger; C050733:2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one
keywords: Allele-specific expression; DIMBOA; QTL mapping; biosynthetic cluster; cis-element; defence; secondary metabolites.