Prune dwarf virus (PDV) is one of the most dangerous pathogens of fruit trees worldwide. One of the most important proteins required for PDV infection is replicase. (P1 protein) which anchored viral RNA and builds replication complex along with RNA depended polymerase. Despite the importance of PDV as a pathogen, our knowledge regarding tissue/cellular localization and structure of PDV P1 protein is still incomplete. The aim of this work was to localize replicase distribution in leaf tissues and cells by immunofluorescent and immunogold labeling of Nicotiana tobaccum cv Samsun and development of a 3D model of PDV replicase. In this paper we demonstrate that PDV replication, is similar to that of Alfalfa mosaic virus and is strongly connected with tonoplasts. In addition, PDV replicase and coat protein (CP) were also found to be strongly associated with membranes of endoplasmic reticulum and, indicating the potential involvement of these membrane structures in the processes related to viral infection. Bioinformatic analyzes based on 3D modeling and structure prediction revealed that P1 protein has a potential transmembrane domain which enables protein anchoring to tonoplast during replication complex assembly.

The one-third of plant viruses are seed transmitted, and this has significant economic consequences. Tobacco rattle virus (TRV), belonging to the genus Tobravirus and family Virgaviridae, has one of the widest host range of any known plant viruses. TRV infects vegetative organ and effects seed and pollen development that results in a decrease in crop yield. The mechanisms by which Tobravirus is transmissible to seeds are still poorly understood. The presence of the virus in pollen grains and inside ovaries is linked with seed transmission and can have effects on virus particles' transport during the pollination and fertilization process. This paper focuses on the significant impact of TRV on pepper and tobacco anthers and ultrastructure changes in ovaries. The presence of two types of TRV particles in ovary wall parenchyma and vascular tissues as well as in placenta cells was demonstrated via ultrastructural analysis. For the first time, the regular inclusion of virus particles was reported in both ovule integuments and nucellus parenchyma cells. Immunolocalization of TRV capsid proteins indicated the deposition of TRV CP epitope in ovary vascular bundles and in placenta cells. Moreover, the presence of virus particles was demonstrated inside pepper seeds in endothelium and integument parenchyma layers as well as on the embryo cell wall. Virus particles were found not only on the surface of pollen grains but also inside pepper pollen protoplasts in mature anthers. Also, this is the first time where TRV particles are reported in both differentiated endothecium cells and the remaining tapetum cells. Moreover, the detection of TRV capsid protein epitope in tobacco and pepper vascular anther tissues as well as in tapetum and endothecium cells was correlated with TRV distribution in infected anthers. Demonstrated analyses indicated that pollen grains and ovaries with ovules as well as could be a natural source of TRV transmission.

Potato plants cv. Rywal with hypersensitivity gene Ny-1 infected with PVY N or PVY NTN reacted in local necroses 3 days after infection. Potato virus Y (PVY) particles were found in epidermis, mesophyll, phloem and xylem cells in inoculated leaves. Noncapsidated virus particles (without capsid protein) were observed already 10 h after infection by using electron microscopy in situ. Capsid protein on one terminus of noncapsidated virus particles was located 5 days after inoculation with the use of immunogold labeling method. Whereas cytoplasmic inclusions were observed for the first time 24 days after infection during hypersensitive response. Ultrastructural studies showed that ER may take part in PVY RNA replication and capsidation of Potyvirus particles. Observed cytopathological changes and virus particles indicate that cell nucleus and mitochondrion might participate in PVY life cycle. During hypersensitive response PVY particles were found in plasmodesmata as well as in phloem and xylem.

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