Zheng Linlin, McMullen Michael D, Bauer Eva, Schön Chris-Carolin, Gierl Alfons, Frey Monika
Lehrstuhl für Genetik, Wissenschaftszentrum Weihenstephan, Technische Universität München, 85354 Freising, Germany.
USDA ARS, University of Missouri, Columbia, MO 65211, USA.
J Exp Bot. 2015 Jul;66(13):3917-30. doi: 10.1093/jxb/erv192. Epub 2015 May 11.
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.
苯并恶嗪类化合物是预先形成的具有保护作用和化感作用的化合物。玉米（Zea mays L.）中的主要苯并恶嗪类化合物是2,4 - 二羟基 - 7 - 甲氧基 - 1,4 - 苯并恶嗪 - 3 - 酮（DIMBOA）。DIMBOA赋予植物对草食动物和微生物的抗性。其保护浓度主要存在于幼苗中。我们利用玉米巢式关联作图（NAM）群体中的遗传多样性，来鉴定在发育后期具有显著苯并恶嗪类化合物浓度的品系。在吸胀后24天（dai），只有包括Mo17在内的三个品系显示出有效的DIMBOA浓度为1.5 mM或更高；相比之下，B73的DIMBOA含量较低。基于Mo17和B73进行了作图研究，以揭示影响24 dai植株中DIMBOA水平的机制。一个主要的数量性状位点定位于位于4号染色体短臂上的Bx基因簇，该基因簇编码DIMBOA生物合成基因。Mo17与所有其他NAM品系的区别在于，在发育后期Bx1基因具有高转录表达。Bx1编码该途径的标志性酶。在24 dai的Mo17×B73杂种中，仅检测到Mo17 Bx1等位基因转录本。一个3.9 kb的顺式元件，称为DICE（远端顺式元件），位于Bx基因簇中Bx1上游约140 kb处，是Mo17发育后期Bx1转录本高水平所必需的。DICE区域是减数分裂重组的热点。遗传分析表明，24 dai时高DIMBOA浓度并不严格依赖于高Bx1转录水平。然而，Bx1在转基因中的组成型表达增加了24 dai时的DIMBOA水平，证实了DIMBOA含量与Bx1转录之间的相关性。
