Does induced phytotoxicity in apple replant disease affect Malus domestica roots?

苹果是世界上最重要的栽培水果之一。在苗圃中，植物被频繁地重新种植（2-3年），这导致作物产量下降，也称为苹果再植病（ARD）。ARD可以被定义为“苹果植物对土壤的有害干扰生理和形态反应，这些土壤由于以前的苹果栽培而面临其（微）生物群系的改变”。以前，生物广谱土壤熏蒸剂用于控制ARD。然而，应用复杂，成本高，对环境和人类健康的危害是一个问题。因此，育种和/或选择不太敏感的基因型将为ARD提供更可持续的解决方案。然而，ARD性状相关标记的发展依赖于更好地理解植物中的分子反应，以解开疾病的病因。最近，植保素生物合成基因被发现强烈上调后，7天的文化ARD土壤相比，消毒ARD土壤。结果表明，植物抗毒素在根系中积累的浓度很高，导致潜在的植物毒性。参与植物抗毒素转运和分泌的ABC转运蛋白没有显示出任何调节，导致假设植物抗毒素在ARD条件下可能不会分泌到土壤中，因此在根中以非常高的浓度积累。此外，液泡运输也可能受到阻碍，导致积累的物质缺乏解毒作用。提出的缺乏植物抗毒素分泌或通过ABC转运蛋白螯合到液泡中的潜在原因可能是在ARD受影响的植物中产生有毒的氰化物水平，导致ABC转运蛋白在ARD根中转运植物抗毒素的ATP可用性降低。本项目的目标是阐明ARD诱导的植物抗毒素在ARD综合征中的作用，并阐明ARD受影响植物中的分子反应。重点将是推断他们在ARD考虑进一步相互作用的基因/蛋白质的作用。将分析化合物的毒性和定位以及解毒机制，例如从细胞质转运。此外，额外的有毒副产物氰化物代谢以及能源供应将进行更密切的调查，以实现ARD的分子机制的详细概述。荧光原位杂交，显微镜，基因表达研究和代谢分析将实现这一目标。敏感和不太敏感的基因型之间的比较将提供知识的早期预测标记的ARD严重程度在土壤中，并将有助于育种计划，以选择ARD耐受苹果植物。

Apple (Malus domestica) is one of the most important cultivated fruits worldwide. In tree nurseries, plants are replanted frequently (2-3 years), which leads to diminished crop productivity, also known as apple replant disease (ARD). ARD can be defined as “a harmfully disturbed physiological and morphological reaction of apple plants to soils that faced alterations in their (micro-) biome due to the previous apple cultures”. Formerly, biologically broad-spectrum soil fumigants were used to control ARD. Nevertheless, application intricacy, high cost and hazards to environment and human health are problematic. Therefore, breeding and/or selecting less sensitive genotypes would present a more sustainable solution to ARD. However, the development of ARD trait associated markers relies on a better understanding of molecular reactions in planta to unravel disease etiology. Recently, phytoalexin biosynthesis genes were found to be strongly up-regulated after seven days of culture on ARD soil compared to disinfected ARD soil. It was revealed that the phytoalexins accumulated in the root system in very high concentrations leading to potential phytotoxicity. ABC transporters which are involved in the translocation and exudation of phytoalexins did not show any regulation leading to the assumption that phytoalexins may not be exuded into the soil under ARD conditions and therefore accumulate in the roots in very high concentrations. Additionally, the vacuolar transport may be hindered as well leading to the lack of detoxification of the accumulated substances. A potential reason for the proposed lack of exudation of phytoalexins or of sequestration into vacuoles via ABC transporters may be the generation of toxic cyanide levels in ARD affected plants leading to less ATP availability for ABC transporters to transport phytoalexins in ARD roots. The goal of the present project is to unravel the role of ARD induced phytoalexins on the ARD syndrome and to elucidate molecular reactions in ARD affected plants. The focus will be on deducing their role in ARD considering further interacting genes/proteins. Toxicity and localization of the compounds will be analyzed as well as detoxification mechanisms, e.g. transport from the cytoplasm. Furthermore, additional toxic byproducts in cyanide metabolism as well as energy supply will be investigated more closely to achieve a detailed overview of molecular mechanisms of ARD. Fluorescence in situ hybridization, microscopy, gene expression studies and metabolic analyses will be employed to achieve this goal. Comparisons between a sensitive and a less sensitive genotype will provide knowledge for the early prediction of markers of ARD severity in soils and will help in breeding programs to select ARD tolerant apple plants.