Spatiotemporal Changes in Xylan-1/Xyloglucan and Xyloglucan Xyloglucosyl Transferase (XTH-Xet5) as a Step-In of Ultrastructural Cell Wall Remodelling in Potato⁻Potato Virus Y (PVY) Hypersensitive and Susceptible Reaction.

One type of monitoring system in a plant cell is the cell wall, which intensively changes its structure during interaction with pathogen-stress factors. The wall plays a role as a dynamic and controlled structure, although it is not fully understood how relevant these modifications are to the molecular mechanisms during plant⁻virus interactions. In this work we localise the non-cellulosic polysaccharides such as xyloglucan, xylan (xylan-1) and xyloglucosyl transferase (XTH-Xet5), the enzyme that participates in the metabolism of xyloglucan. This provided us with information about the in situ distribution of the components of the hemicellulotic cell wall matrix in hypersensitive and susceptible potato⁻PVY interactions. The loosening of the cell wall was accompanied by an increase in xylan depositions during susceptible interactions, whereas, during the hypersensitive response, when the cell wall was reinforced, the xylan content decreased. Moreover, the PVY inoculation significantly redirected XTH-Xet5 depositions, regardless of types of interactions, compared to mock-inoculated tissues. Furthermore, the immunogold localisation clearly revealed the domination of Xet5 in the cell wall and in vesicles in the susceptible host. In contrast, in the resistant host increased levels of Xet5 were observed in cytoplasm, in the cell wall and in the trans-Golgi network. These findings show that the hypersensitive reaction activated XTH-Xet5 in the areas of xyloglucan endo-transglycosylase (XET) synthesis, which was then actively transported to cytoplasm, cell wall and to vacuoles. Our results provide novel insight into cell wall reorganisation during PVY infection as a response to biotic stress factors. These novel findings help us to understand the mechanisms of defence responses that are incorporated into the cell wall signalling network.