Interaction of the Beet necrotic yellow vein virus with the auxin pathway in Beta vulgaris – Investigations on the molecular mechanism and impact on pathogenicity, symptom development and viral spread.

甜菜坏死黄脉病毒（Beetnecrotiveyellowveinvirus，BNYVV）是甜菜丛根病（Rhizomania）的病原，是由甜菜多黏菌（Polymyxabetae）传播的甜菜病毒性病害。在BNYVV感染后，植物显示大量侧根增殖，导致“根须”的特征症状和主根重量降低。生长素作为植物的主要激素，控制着包括侧根发育在内的一系列发育过程。因此，推测BNYVV与生长素信号通路相互作用以诱导侧根增殖，但负责这一过程的机制尚不清楚。初步研究表明，在甜菜中发现了一个与BNYVV致病因子P25相互作用的生长素/吲哚乙酸（Aux/IAA）转录因子。Aux/IAA蛋白是一种转录抑制因子，在细胞核中调控生长素反应基因的表达。P25通过从细胞核重新定位到细胞质中来中断Aux/IAA蛋白的活性。重定位之后是大量上调参与侧根形成的生长素反应基因。这些结果首次证明了甜菜花叶病毒与甜菜生长素信号通路相互作用。现在，这项拟议研究的目的是详细研究这种相互作用，特别关注分子机制以及对致病性、症状发展和病毒传播的影响。为此，将测试由甜菜基因组编码的所有Aux/IAA蛋白与P25的相互作用。此外，与Aux/IAA蛋白相互作用的结构域将被鉴定，以增加我们对病毒蛋白多功能性质的了解。本研究将利用BNYVV的全长cDNA克隆，研究BNYVV与生长素信号通路的互作对甜菜致病性和症状发展的影响。此外，我们还将建立一个针对甜菜的病毒诱导基因沉默系统来沉默特定的Aux/IAA基因，以模拟P25的再定位，并揭示其对侧根形成和基因表达的影响。由于尚不清楚载体甜菜夜蛾侧根形成的生物学相关性，因此还旨在证明是否对病毒获得和载体繁殖有影响。该项目的结果将提供一个深入了解BNYVV和其宿主甜菜之间的相互作用。此外，与病毒因子相互作用的植物蛋白的鉴定提供了新的靶标，可用于通过基因组编辑开发新的抗性因子。

Beet necrotic yellow vein virus (BNYVV) is the causal agent of Rhizomania, a viral disease of sugar beet with high economic importance transmitted by the plasmodiophorid Polymyxa betae. Upon BNYVV infection, plants display massive lateral root proliferation leading to the characteristic symptom of a “root beard” and reduced tap root weight. Auxin as the major plant hormone controls an array of developmental processes including the development of lateral roots. Therefore, it is supposed that BNYVV interacts with the auxin signaling pathway to induce lateral root proliferation but the mechanism responsible for that is still unknown. In preliminary experiments, an auxin/indole-3-acetic acid (Aux/IAA) transcription factor interacting with the pathogenicity factor of BNYVV (P25) could be identified in sugar beet. Aux/IAA proteins are transcriptional repressor that regulate the expression of auxin responsive genes in the nucleus. P25 interrupts the activity of the Aux/IAA proteins by a relocalization from the nucleus into the cytoplasma. The relocalization is followed by a massive upregulation of auxin responsive genes involved in lateral root formation. The results provide for the first time evidence that BNYVV interacts with the auxin signaling pathway in sugar beet. It is now the aim of this proposed study to investigate this interaction in detail with particular focus on the molecular mechanism and the impact on pathogenicity, symptom development and viral spread. For this purpose, all Aux/IAA proteins encoded by the sugar beet genome will be tested for an interaction with P25. Furthermore, the domain interacting with Aux/IAA proteins shall be identified in order to increase our knowledge about the multifunctional nature of viral proteins. A full length cDNA clone of BNYVV will be applied to study the effects of the interaction with the auxin signaling pathway on pathogenicity and symptom development in sugar beet. Apart from that, a virus-induced gene silencing system developed for sugar beet will be used to silence specific Aux/IAA genes in order to mimic the relocalization by P25 and to reveal the effect on lateral root formation and gene expression. Since the biological relevance of the lateral root formation for the vector P. betae is not known yet, it is also aimed to prove whether there is an effect on virus acquisition and vector propagation. The project results will provide a deep insight into the interaction between BNYVV and its host sugar beet. Moreover, the identification of plant proteins interacting with viral factors provides new targets that can be utilized to develop new resistance factors by genome editing.