Chair of Plant Breeding, Technical University of Munich, Liesel-Beckman Str. 2, 85354, Freising, Germany.
Associate Professorship of Biotechnology of Natural Products, Technical University of Munich, Liesel-Beckmann Str. 1, 85354, Freising, Germany.
Phytochemistry. 2021 Dec;192:112947. doi: 10.1016/j.phytochem.2021.112947. Epub 2021 Sep 15.
Plant specialised metabolites constitute a layer of chemical defence. Classes of the defence compounds are often restricted to a certain taxon of plants, e.g. benzoxazinoids (BX) are characteristically detected in grasses. BXs confer wide-range defence by controlling herbivores and microbial pathogens and are allelopathic compounds. In the crops maize, wheat and rye high concentrations of BXs are synthesised at an early developmental stage. By transfer of six Bx-genes (Bx1 to Bx5 and Bx8) it was possible to establish the biosynthesis of 2,4-dihydroxy-1,4-benzoxazin-3-one glucoside (GDIBOA) in a concentration of up to 143 nmol/g dry weight in Arabidopsis thaliana. Our results indicate that inefficient channeling of substrates along the pathway and metabolisation of intermediates in host plants might be a general drawback for transgenic establishment of specialised metabolite biosynthesis pathways. As a consequence, BX levels required for defence are not obtained in Arabidopsis. We could show that indolin-2-one (ION), the first specific intermediate, is phytotoxic and is metabolised by hydroxylation and glycosylation by a wide spectrum of plants. In Arabidopsis, metabolic stress due to the enrichment of ION leads to elevated levels of salicylic acid (SA) and in addition to its intrinsic phytotoxicity, ION affects plant morphology indirectly via SA. We could show that Bx3 has a crucial role in the evolution of the pathway, first based on its impact on flux into the pathway and, second by C3-hydroxylation of the phytotoxic ION. Thereby BX3 interferes with a supposedly generic detoxification system towards the non-specific intermediate.
植物特化代谢物构成了一层化学防御。防御化合物的类别通常局限于某一植物类群，例如苯并恶嗪类（BX）在禾本科植物中特征性地被检测到。BX 通过控制食草动物和微生物病原体并作为化感化合物赋予广泛的防御作用。在玉米、小麦和黑麦等作物中，BXs 在早期发育阶段合成高浓度的 BXs。通过转移六个 Bx 基因（Bx1 到 Bx5 和 Bx8），可以在拟南芥中建立高达 143 nmol/g 干重的 2,4-二羟基-1,4-苯并恶嗪-3-酮葡萄糖苷（GDIBOA）的生物合成。我们的结果表明，沿途径的底物效率低下和中间产物在宿主植物中的代谢可能是特化代谢物生物合成途径转基因建立的一般缺陷。因此，在拟南芥中无法获得用于防御所需的 BX 水平。我们表明，吲唑-2-酮（ION），第一个特定的中间产物，是植物毒性的，并且被多种植物通过羟化和糖基化代谢。在拟南芥中，由于 ION 的富集导致代谢应激，导致水杨酸（SA）水平升高，并且由于其内在的植物毒性，ION 通过 SA 间接影响植物形态。我们表明 Bx3 在途径的进化中具有关键作用，首先基于其对途径通量的影响，其次基于其对植物毒性 ION 的 C3-羟化作用。由此，BX3 干扰了针对非特异性中间产物的假定通用解毒系统。
