Complete genome sequence of a divergent strain of potato virus P isolated from Solanum tuberosum in Russia.

Contigs with sequence similarity to potato virus P (PVP), which belongs to the genus Carlavirus, were identified by high-throughput sequencing analysis in potato tubers collected from a farmer's potato production field in Surazhevka, Artyom, Primorskiy Krai (Russia) in 2018. The complete genome sequence of this virus consisted of 8,394 nucleotides, excluding the poly(A) tail. This is the first report of PVP being detected outside South America. The isolate had high sequence similarity to PVP isolates from Argentina and Brazil, but low sequence similarity was observed in the genes encoding the RNA-dependent RNA polymerase (69% nucleotide sequence identity and 80% amino acid sequence identity) and coat protein (78% nucleotide sequence identity and 89% amino acid sequence identity). Phylogenetic analysis revealed that this PVP-like virus clustered with known PVP isolates but was distinct from them. Comparison of the sequences using the classification criteria of the ICTV indicated that this PVP-like virus is a strain of PVP.

Influence of the terminal left domain on horizontal and vertical transmissions of tomato planta macho viroid and potato spindle tuber viroid through pollen.

Viroids can be transmitted vertically and/or horizontally by pollen. Tomato planta macho viroid (TPMVd) has a high rate of horizontal transmission by pollen, whereas potato spindle tuber viroid (PSTVd) does not. To specify the domain(s) involved in horizontal transmission, four viroid chimeras were created by exchanging the terminal left (TL) and/or pathogenicity (P) domains between PSTVd and TPMVd. PSTVd-based chimeras containing TPMVd-TL and P, or TPMVd-TL alone, displayed a high rate of horizontal transmission. TPMVd-based chimeras containing PSTVd-TL and P lost infectivity, and those containing PSTVd-TL alone displayed a low rate of horizontal transmission. In addition, the vertical transmission rate was also higher in the mutants containing TPMVd-TL than in the others. These findings indicate that the sequences or structures in the TL and P (although the role is limited) domains are important not only for horizontal but also for vertical transmission by pollen.

Vertical and Horizontal Transmission of Pospiviroids.

Viroids are highly structured, single-stranded, non-protein-coding circular RNA pathogens. Some viroids are vertically transmitted through both viroid-infected ovule and pollen. For example, potato spindle tuber viroid, a species that belongs to Pospiviroidae family, is delivered to the embryo through the ovule or pollen during the development of reproductive tissues before embryogenesis. In addition, some of Pospiviroidae are also horizontally transmitted by pollen. Tomato planta macho viroid in pollen infects to the ovary from pollen tube during pollen tube elongation and eventually causes systemic infection, resulting in the establishment of horizontal transmission. Furthermore, fertilization is not required to accomplish the horizontal transmission. In this review, we will overview the recent research progress in vertical and horizontal transmission of viroids, mainly by focusing on histopathological studies, and also discuss the impact of seed transmission on viroid dissemination and seed health.

Differences in dynamics of horizontal transmission of Tomato planta macho viroid and Potato spindle tuber viroid after pollination with viroid-infected pollen.

For viroids, pollen transmission is an important transmission pathway to progeny seeds and new hosts. In the current study, we found that Tomato planta macho viroid (TPMVd)-but not Potato spindle tuber viroid (PSTVd)-was horizontally transmitted by pollen from petunia plants. Using tissue-printing hybridization to track the changes in viroid distribution after pollination, we noted that TPMVd was present in petunia stigma, styles, and eventually ovaries, whereas PSTVd was detected in the stigma and upper style but not the ovary. These findings suggest that horizontal transmission of viroids depends on the infection of the lower style and ovary during the elongation of pollen tubes after pollination. Additionally, TPMVd was transmitted horizontally, leading to systematic infection, when we used TPMVd-infected petunia pollen to pollinate the flowers of healthy tomato plants. Fertilization typically does not occur after heterologous pollination and thus likely is not required to accomplish horizontal transmission of viroids.

Distribution of Tomato planta macho viroid in germinating pollen and transmitting tract.

Vertical and horizontal pollen transmission is important for efficient infection by viroids. Vertical pollen transmission of viroids is attributed to the infection by viroid in the embryo sac through infected pollen. To identify the viroid infection in pollen and pollen tubes elongating through the transmitting tract, we used in situ hybridization to histochemically analyze the distribution of Tomato planta macho viroid (TPMVd) in pollen grains, the stigma, and style of petunia plants. TPMVd was present in the generative nucleus and vegetative nucleus of mature infected pollen grains and germinating pollen grains. During pollen tube growth, TPMVd was present in the vegetative nucleus and two sperm nuclei, which were generated by division of the generative nucleus in the style transmitting tract. These findings indicated that viroid infection in sperm nuclei is responsible for vertical pollen transmission of viroids. TPMVd infection from TPMVd-infected pollen tubes to the transmitting tract was not observed. In addition, TPMVd signals were not confirmed in the stigma and transmitting tract of TPMVd-infected petunia plants, suggesting that viroids may not replicate in these tissues at the stage of mature style. Therefore, TPMVd may leak from the pollen tube somewhere in the ovary, except in the transmitting tract, during the horizontal transmission of TPMVd.

Histone deacetylase inhibitors relieve morphine resistance in neuropathic pain after peripheral nerve injury.

Neuropathic pain is often insensitive to morphine. Our previous study has demonstrated that neuron-restrictive silencer factor represses mu opioid receptor (MOP) gene expression in the dorsal root ganglion (DRG) via histone hypoacetylation-mediated mechanisms after peripheral nerve injury, thereby causing loss of peripheral morphine analgesia. Here, we showed that histone deacetylase (HDAC) inhibitors, such as trichostatin A and valproic acid, restored peripheral and systemic morphine analgesia in neuropathic pain. Also, these agents blocked nerve injury-induced MOP down-regulation in the DRG. These results suggest that HDAC inhibitors could serve as adjuvant analgesics to morphine for the management of neuropathic pain.

Distribution of potato spindle tuber viroid in reproductive organs of petunia during its developmental stages.

Embryo infection is important for efficient seed transmission of viroids. To identify the major pattern of seed transmission of viroids, we used in situ hybridization to histochemically analyze the distribution of Potato spindle tuber viroid (PSTVd) in each developmental stage of petunia (flowering to mature seed stages). In floral organs, PSTVd was present in the reproductive tissues of infected female × infected male and infected female × healthy male but not of healthy female × infected male before embryogenesis. After pollination, PSTVd was detected in the developed embryo and endosperm in all three crosses. These findings indicate that PSTVd is indirectly delivered to the embryo through ovule or pollen during the development of reproductive tissues before embryogenesis but not directly through maternal tissues as cell-to-cell movement during embryogenesis.