Summary

Potato is one of the most important crops with yearly production of about 350 million tons. Potato virus Y (PVY) is the most economically devastating plant virus affecting the potato production worldwide (Kreuze et al., 2020). One of the major concerns for potato growers is the PVYNTN strain being the most aggressive PVY isolate, which is outcompeting other isolates on the field and is able to induce potato tuber necrotic ringspot disease (PTNRD) in potato tubers. The reduction in tuber marketable yield can reach up to 80%. Due to its economic impact, extensive programs have been developed to control and manage the PVY infection, however the virus still represents an ongoing challenge (Lacomme and Jacquot, 2017).

As an intracellular parasite, viruses depend on the molecular machinery of the plant cells. Therefore, to complete its infection cycle, the virus reprograms the intracellular environment of the host. A complex and dynamic interaction network is established between viral and plant proteins. Understanding the plant-virus interaction is essential for the development of sustainable and efficient plant protection strategies.

During the last years, technical and computational advances helped us to better understand the large interaction networks. The use of systems biology approach has shown to be a powerful tool to reveal molecular basis of plant defence response. At NIB, we built the potato knowledge network and a mechanistic model of defence signalling (Miljkovic et al., 2012; Ramsak et al., 2018). Together with the use of large omics datasets, the analysis of knowledge network disclosed an unknown connection between ethylene and salicylic acid signalling (Ramsak et al., 2018). On the other hand, structural studies of viral proteins shed some light on the roles of some PVY proteins. In line with this, we recently determined the high-resolution cryoelectron microscopy (cryo-EM) structure of the PVY virions, which reveal important features of coat protein (CP) structure for understanding its multifunctional nature as well as its complex and compact assembly into flexuous and filamentous viral particles (Kežar et al., 2019). Similarly, structure of another PVY protein, the viral protein genome-linked (VPg), was determined (Coutinho de Oliveira et al., 2019).

However, the plant cell-PVY protein interaction network is still poorly understood and the dynamic nature of this interactome has not been addressed yet. Namely, the interactions change during the course of the viral life cycle; they are dynamic both in time and space (see review Mäkinen and Hafrén, 2014). Thus, it is important to address and understand also this aspect in studies of plant-virus interactions (Rodrigo et al., 2017). In order to uncover the subcellular localisation, the timing and the protein complexes involved in different steps of the viral cycle, a sophisticated combination of research methods has to be exploited. This knowledge will help, not only to understand the necessary mechanisms required to establish an infection cycle and how the virus manipulates the plant machinery, but also to shed light on plant pathways that contribute to disease development.

The aim of the proposed research project is to better understand the complex mechanism of PVY infection cycle. Special emphasis will be put on studying the viral cell-to-cell movement and how the virus hijacks the host’s machinery to carry out a successful infective cycle.

We hypothesise that the dynamic changes of the plant-virus interaction network are crucial for a successful infection.

In order to attest it, we have set the following specific objectives:

  • Identification of sites in viral coat protein critical for cell-to-cell movement
  • Obtaining structural data of protein complexes associated with a successful viral cycle
  • Dissecting the structure/function relationship of selected multitasking PVY proteins involved in viral-host protein complexes
  • Screening for new plant components involved in the interaction network established between PVY and its host during infection
  • Identification of new properties of interaction network through interrogation of improved plant immune signalling model

We will combine structural analysis and in planta functional studies, using state-of-the-art technologies, to explore the interaction network of viral and host components involved in different stages of the infection. The infection cycle is tightly spatiotemporally regulated, thus part of the information is missing when investigating the static picture of the interaction. We will use non-invasive cell imaging protocols that are being under development within the current ARRS project J4-1777 and the sampling approach of small tissue sections that was optimised during the recently finished ARRS project J4-7636. Both methods will allow us to capture the dynamic changes of the infection cycle.

The project will help to better understand the PVY mode of action, how the different stages of the virus multiplication cycle are localised and coordinated within the plant cell and the role of viral and host proteins in such interconnected pathways. This knowledge is crucial for developing effective agricultural management strategies. On the other hand, it will provide us with potential host targets for crop breeding programmes.

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