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

苹果(Malus Home Tica)是世界上最重要的栽培水果之一。在苗圃中，植物频繁重植(2-3年)，导致作物产量下降，也被称为苹果再植病(ARD)。ARD可以被定义为“苹果植物对土壤的一种有害的生理和形态反应，由于以前的苹果培养，这些土壤面临着它们(微)生物群的变化”。以前，生物广谱土壤熏蒸剂被用来控制ARD。然而，应用复杂、成本高以及对环境和人类健康的危害是有问题的。因此，培育和/或选择不太敏感的基因将为ARD提供一种更可持续的解决方案。然而，ARD特征相关标记的发展依赖于对植物中分子反应的更好理解，以揭示疾病病因学。最近，与消毒的ARD土壤相比，在ARD土壤上培养7天后，植物保卫素生物合成基因被发现强烈上调。结果表明，植物防御素在根系中以很高的浓度积累，具有潜在的药害作用。参与植物保卫素转运和分泌的ABC转运蛋白没有表现出任何调节作用，从而导致假设在ARD条件下，植物保卫素可能不会渗入土壤，因此在根中以很高的浓度积累。此外，液泡的运输也可能受到阻碍，导致积累的物质缺乏解毒作用。一个潜在的原因可能是在受ARD影响的植物中产生了有毒的氰化物，导致ABC转运蛋白在ARD根中运输植物保卫素的可获得性降低。本项目的目标是揭示ARD诱导的植物保卫素在ARD综合征中的作用，并阐明受ARD影响的植物中的分子反应。重点将放在考虑进一步相互作用的基因/蛋白质的情况下，推断它们在ARD中的作用。将分析化合物的毒性和定位以及解毒机制，例如从细胞质运输。此外，将对氰化物代谢和能源供应中的其他有毒副产物进行更密切的调查，以实现对ARD分子机制的详细概述。为了实现这一目标，将采用荧光原位杂交、显微镜、基因表达研究和代谢分析。比较敏感和不敏感的基因将为早期预测土壤中ARD严重程度的标记提供知识，并将有助于选育耐ARD苹果植株。

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.