AtGSTU19 and AtGSTU24 as Moderators of the Response of Arabidopsis thaliana to Turnip mosaic virus

Plants produce glutathione as a response to the intercellular redox state. Glutathione actively participates in the reactive oxygen species (ROS)-dependent signaling pathway, especially under biotic stress conditions. Most of the glutathione S-transferases (GSTs) are induced in cells during the defense response of plants not only through highly specific glutathione-binding abilities but also by participating in the signaling function. The tau class of GSTs has been reported to be induced as a response under stress conditions. Although several studies have focused on the role of the tau class of GSTs in plant–pathogen interactions, knowledge about their contribution to the response to virus inoculation is still inadequate. Therefore, in this study, the response of Atgstu19 and Atgstu24 knockout mutants to mechanical inoculation of Turnip mosaic virus (TuMV) was examined. The systemic infection of TuMV was more dynamically promoted in Atgstu19 mutants than in wild-type (Col-0) plants, suggesting the role of GSTU19 in TuMV resistance. However, Atgstu24 mutants displayed virus limitation and downregulation of the relative expression of TuMV capsid protein, accompanied rarely by TuMV particles only in vacuoles, and ultrastructural analyses of inoculated leaves revealed the lack of virus cytoplasmic inclusions. These findings indicated that Atgstu24 mutants displayed a resistance-like reaction to TuMV, suggesting that GSTU24 may suppress the plant resistance. In addition, these findings confirmed that GSTU1 and GSTU24 are induced and contribute to the susceptible reaction to TuMV in the Atgstu19–TuMV interaction. However, the upregulation of GSTU19 and GSTU13 highly correlated with virus limitation in the resistance-like reaction in the Atgstu24–TuMV interaction. Furthermore, the highly dynamic upregulation of GST and glutathione reductase (GR) activities resulted in significant induction (between 1 and 14 days post inoculation [dpi]) of the total glutathione pool (GSH + GSSG) in response to TuMV, which was accompanied by the distribution of active glutathione in plant cells. On the contrary, in Atgstu19, which is susceptible to TuMV interaction, upregulation of GST and GR activity only up to 7 dpi symptom development was reported, which resulted in the induction of the total glutathione pool between 1 and 3 dpi. These observations indicated that GSTU19 and GSTU24 are important factors in modulating the response to TuMV in Arabidopsis thaliana. Moreover, it was clear that glutathione is an important component of the regulatory network in resistance and susceptible response of A. thaliana to TuMV. These results help achieve a better understanding of the mechanisms regulating the Arabidopsis–TuMV pathosystem

Ultrastructural effects of PVYNTN infection of <em>Capsicum annuum</em> L. cv. Yolo Wonder generative organs; a first step in describing seed transmission

Potato virus Y NTN (PVYNTN), a member of the family Potyviridae, is one of the most important plant viruses. Despite common occurrence of seed transmission process in the Potyviridae, the number or routes of virion entry into seeds are still unclear. Embryos could probably be infected either through host embryogenesis processes or via infection of reproductive tissues, therefore both processes of virus transmission in seeds and pollen grains are likely to be related. Infection by PVY has been studied in detail in host vegetative organs. We investigated, for the first time the impact of infection by the necrotic strain of PVY on Capsicum annuum reproductive organs. We found PVYNTN particles inside C. annuum pollen grains and on the exine surfaces, and PVY epitopes were also found in pollen tubes. We postulate that the male gametophyte in C. annuum could be a source of PVY infection, which may have significance in self-pollinated hosts. We also demonstrated that PVYNTN particles could be detected inside C. annuum seeds on embryo surfaces, while particles and Potyvirus inclusion bodies were observed in endothelium layers. These were mainly detected inside ovarian tissues, that is, in the ovular integuments and nucelli. Changes in both gametophytes strongly indicate that generative organs were a source of PVYNTN infection. Furthermore, we have demonstrated that in C. annuum, PVY was transmitted vertically via seeds

Ultrastructural effects of PVYNTN infection of Capsicum annuum L. cv. Yolo Wonder generative organs; a first step in describing seed transmission

Potato virus Y NTN (PVYNTN), a member of the family Potyviridae, is one of the most important plant viruses. Despite common occurrence of seed transmission process in the Potyviridae, the number or routes of virion entry into seeds are still unclear. Embryos could probably be infected either through host embryogenesis processes or via infection of reproductive tissues, therefore both processes of virus transmission in seeds and pollen grains are likely to be related. Infection by PVY has been studied in detail in host vegetative organs. We investigated, for the first time the impact of infection by the necrotic strain of PVY on Capsicum annuum reproductive organs. We found PVYNTN particles inside C. annuum pollen grains and on the exine surfaces, and PVY epitopes were also found in pollen tubes. We postulate that the male gametophyte in C. annuum could be a source of PVY infection, which may have significance in self-pollinated hosts. We also demonstrated that PVYNTN particles could be detected inside C. annuum seeds on embryo surfaces, while particles and Potyvirus inclusion bodies were observed in endothelium layers. These were mainly detected inside ovarian tissues, that is, in the ovular integuments and nucelli. Changes in both gametophytes strongly indicate that generative organs were a source of PVYNTN infection. Furthermore, we have demonstrated that in C. annuum, PVY was transmitted vertically via seeds

Glutathione Modulation in PVY^NTN Susceptible and Resistant Potato Plant Interactions

Glutathione is a metabolite that plays an important role in plant response to biotic stress through its ability to remove reactive oxygen species, thereby limiting the degree of potential oxidative damage. It can couple changes in the intracellular redox state to the development, especially the defense responses, of plants. Several studies have focused on measuring glutathione levels in virus infected plants, but have not provided complete information. Therefore, we analyzed, for the first time, the content of glutathione as well as its ultrastructural distribution related to susceptible and hypersensitive potato–Potato virus Y NTN (PVYNTN) interaction, with an aim of providing new insight into interactive responses to PVYNTN stress. Our findings reported that the inoculation of PVYNTN caused a dynamic increase in the content of glutathione, not only in resistance but also in susceptible reaction, especially at the first steps of plant–virus interaction. Moreover, the increase in hypersensitive response was much more dynamic, and accompanied by a significant reduction in the content of PVYNTN. By contrast, in susceptible potato Irys, the content of glutathione decreased between 7 and 21 days after virus inoculation, which led to a significant increase in PVYNTN concentration. Additionally, our findings clearly indicated the steady induction of two selected potato glutathione S-transferase StGSTF1 and StGSTF2 genes after PVYNTN inoculation, regardless of the interaction type. However, the relative expression level of StGSTF1 did not significantly differ between resistant and susceptible plants, whereas the relative expression levels of StGSTF2 differed between susceptible and resistant reactions. Therefore, we proposed that StGSTF2 can act as a marker of the type of response to PVYNTN. Our observations indicated that glutathione is an important component of signaling as well as the regulatory network in the PVYNTN–potato pathosystem. In resistance responses to PVYNTN, this metabolite activates plant defenses by reducing potential damage to the host plant cell, causing a reduction in virus concentration, while it can also be involved in the development of PVYNTN elicited symptoms, as well as limiting oxidative stress, leading to systemic infection in susceptible potato plants

Molecular Biology of Prune Dwarf Virus—A Lesser Known Member of the Bromoviridae but a Vital Component in the Dynamic Virus–Host Cell Interaction Network

Prune dwarf virus (PDV) is one of the members of Bromoviridae family, genus Ilarvirus. Host components that participate in the regulation of viral replication or cell-to-cell movement via plasmodesmata are still unknown. In contrast, viral infections caused by some other Bromoviridae members are well characterized. Bromoviridae can be distinguished based on localization of their replication process in infected cells, cell-to-cell movement mechanisms, and plant-specific response reactions. Depending upon the genus, “genome activation” and viral replication are linked to various membranous structures ranging from endoplasmic reticulum, to tonoplast. In the case of PDV, there is still no evidence of natural resistance sources in the host plants susceptible to virus infection. Apparently, PDV has a great ability to overcome the natural defense responses in a wide spectrum of plant hosts. The first manifestations of PDV infection are specific cell membrane alterations, and the formation of replicase complexes that support PDV RNA replication inside the spherules. During each stage of its life cycle, the virus uses cell components to replicate and to spread in whole plants, within the largely suppressed cellular immunity environment. This work presents the above stages of the PDV life cycle in the context of current knowledge about other Bromoviridae members