von Rad U, Hüttl R, Lottspeich F, Gierl A, Frey M
Lehrstuhl für Genetik, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany.
Plant J. 2001 Dec;28(6):633-42. doi: 10.1046/j.1365-313x.2001.01161.x.
Benzoxazinoids are major compounds involved in chemical defence in grasses. These toxins are stored in the vacuole as glucosides. Two glucosyltransferases, BX8 and BX9, that catalyse this last step of benzoxazinoid biosynthesis have been isolated via functional cloning. No close relative of these maize genes was found among the known glucosyltransferases. The enzymes display a very high degree of substrate specificity. DIMBOA, the major benzoxazinoid in young maize, is the preferred substrate. Both genes are highly expressed in young maize seedlings, the developmental stage with the highest activity of benzoxazinoid biosynthesis. Bx8 is included in the cluster of DIMBOA biosynthesis genes located on the short arm of chromosome 4. Hence, the gene cluster comprises three different enzymatic functions and a complete set of genes for the biosynthesis of DIBOA glucoside. Bx9 mapped to chromosome 1. Expression of Bx8 and Bx9 in Arabidopsis corroborated the potency of the enzymes in detoxification of their substrates. This capacity might have implications for allelopathic interactions.
苯并恶嗪类化合物是禾本科植物化学防御中的主要化合物。这些毒素以糖苷的形式储存在液泡中。通过功能克隆分离出了两种催化苯并恶嗪类生物合成最后一步的葡萄糖基转移酶，即BX8和BX9。在已知的葡萄糖基转移酶中未发现这些玉米基因的近亲。这些酶表现出非常高的底物特异性。DIMBOA是嫩玉米中的主要苯并恶嗪类化合物，是首选底物。这两个基因在嫩玉米幼苗中高度表达，而嫩玉米幼苗是苯并恶嗪类生物合成活性最高的发育阶段。Bx8包含在位于4号染色体短臂上的DIMBOA生物合成基因簇中。因此，该基因簇包含三种不同的酶功能以及一套完整的用于合成DIBOA葡萄糖苷的基因。Bx9定位于1号染色体。BX8和BX9在拟南芥中的表达证实了这些酶对其底物的解毒能力。这种能力可能对化感相互作用有影响。
