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.

甜菜坏死性黄脉病毒(BNYVV)是甜菜根枯病的病原，由甜菜多粘虫传播，是一种经济价值很高的甜菜病毒病。在BNYVV感染后，植物表现出大量的侧根增殖，导致典型的“根须”症状，并减少了自来根的重量。生长素作为主要的植物激素，控制着包括侧根发育在内的一系列发育过程。因此，BNYVV被认为与生长素信号通路相互作用，诱导侧根增殖，但其机制尚不清楚。在初步实验中，可以在甜菜中鉴定到一个与BNYVV致病因子(P25)相互作用的生长素/吲哚-3-乙酸(AUX/IAA)转录因子。AUX/IAA蛋白是一种转录抑制因子，在细胞核中调节生长素反应基因的表达。P25通过将AUX/IAA蛋白从细胞核重新定位到细胞质来阻断AUX/IAA蛋白的活性。在重新定位之后，与侧根形成有关的生长素反应基因大量上调。这些结果首次为甜菜BNYVV与生长素信号通路的相互作用提供了证据。现在这项拟议的研究的目的是详细地研究这种相互作用，特别是分子机制及其对致病性、症状发展和病毒传播的影响。为此，将测试甜菜基因组编码的所有AUX/IAA蛋白与P25的相互作用。此外，应确定与AUX/IAA蛋白相互作用的结构域，以增加我们对病毒蛋白多功能性质的了解。利用BNYVV的全长cDNA克隆，研究与生长素信号通路的相互作用对甜菜致病性和症状发展的影响。此外，为甜菜开发的病毒诱导的基因沉默系统将被用来沉默特定的Aux/IAA基因，以模拟P25的重新定位，并揭示其对侧根形成和基因表达的影响。由于甜菜病媒体侧根形成的生物学相关性尚不清楚，因此也旨在证明是否对病毒的获取和传播有影响。该项目的结果将为BNYVV与其寄主甜菜之间的相互作用提供深入的见解。此外，与病毒因子相互作用的植物蛋白的鉴定为通过基因组编辑开发新的抗性因子提供了新的靶点。

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.