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Summary: In plants, autophagy is involved in responses to viral infection. However, the role of host factors in mediating autophagy to suppress viruses is poorly understood.A previously uncharacterized plant protein, NbP3IP, was shown to interact with p3, an RNA‐silencing suppressor protein encoded by Rice stripe virus (RSV), a negative‐strand RNA virus. The potential roles of NbP3IP in RSV infection were examined.NbP3IP degraded p3 through the autophagy pathway, thereby affecting the silencing suppression activity of p3. Transgenic overexpression of NbP3IP conferred resistance to RSV infection in Nicotiana benthamiana. RSV infection was promoted in ATG5‐ or ATG7‐silenced plants and was inhibited in GAPC‐silenced plants where autophagy was activated, confirming the role of autophagy in suppressing RSV infection. NbP3IP interacted with NbATG8f, indicating a potential selective autophagosomal cargo receptor role for P3IP. Additionally, the rice NbP3IP homolog (OsP3IP) also mediated p3 degradation and interacted with OsATG8b and p3.Through identification of the involvement of P3IP in the autophagy‐mediated degradation of RSV p3, we reveal a new mechanism to antagonize the infection of RSV, and thereby provide the first evidence that autophagy can play an antiviral role against negative‐strand RNA viruses. [ABSTRACT FROM AUTHOR]

Abstract Background RNA interference (RNAi) in animals and post-transcriptional gene silencing (PTGS) in plants are related phenomena whose functions include the developmental regulation of gene expression and protection from transposable elements and viruses. Plant viruses respond by expressing suppressor proteins that interfere with the PTGS system. Results Here we demonstrate that both transient and constitutive expression of the Tobacco etch virus HC-Pro silencing suppressor protein, which inhibits the maintenance of PTGS in plants, prevents dsRNA-induced RNAi of a lacZ gene in cultured Drosophila cells. Northern blot analysis of the RNA present in Drosophila cells showed that HC-Pro prevented degradation of lacZ RNA during RNAi but that there was accumulation of the short (23nt) RNA species associated with RNAi. A mutant HC-Pro that does not suppress PTGS in plants also does not affect RNAi in Drosophila. Similarly, the Cucumber mosaic virus 2b protein, which inhibits the systemic spread of PTGS in plants, does not suppress RNAi in Drosophila cells. In addition, we have used the Drosophila system to demonstrate that the 16K cysteine-rich protein of Tobacco rattle virus, which previously had no known function, is a silencing suppressor protein. Conclusion These results indicate that at least part of the process of RNAi in Drosophila and PTGS in plants is conserved, and that plant virus silencing suppressor proteins may be useful tools to investigate the mechanism of RNAi.

The chloroplast protein ferredoxin 1 (FD1), with roles in the chloroplast electron transport chain, is known to interact with the coat proteins (CPs) of Tomato mosaic virus and Cucumber mosaic virus. However, our understanding of the roles of FD1 in virus infection remains limited. Here, we report that the Potato virus X (PVX) p25 protein interacts with FD1, whose mRNA and protein levels are reduced by PVX infection or by transient expression of p25. Silencing of FD1 by Tobacco rattle virus -based virus-induced gene silencing (VIGS) promoted the local and systemic infection of plants by PVX. Use of a drop-and-see (DANS) assay and callose staining revealed that the permeability of plasmodesmata (PDs) was increased in FD1 -silenced plants together with a consistently reduced level of PD callose deposition. After FD1 silencing, quantitative reverse transcription–real-time PCR (qRT–PCR) analysis and LC-MS revealed these plants to have a low accumulation of the phytohormones abscisic acid (ABA) and salicylic acid (SA), which contributed to the decreased callose deposition at PDs. Overexpression of FD1 in transgenic plants manifested resistance to PVX infection, but the contents of ABA and SA, and the PD callose deposition were not increased in transgenic plants. Overexpression of FD1 interfered with the RNA silencing suppressor function of p25. These results demonstrate that interfering with FD1 function causes abnormal plant hormone-mediated antiviral processes and thus enhances PVX infection. [ABSTRACT FROM AUTHOR]

Background: Plant feeding, free-living nematodes cause extensive damage to plant roots by direct feeding and, in the case of some trichodorid and longidorid species, through the transmission of viruses. Developing more environmentally friendly, target-specific nematicides is currently impeded by slow and laborious methods of toxicity testing. Here, we developed a bioactivity assay based on the dynamics of light 'speckle' generated by living cells and we demonstrate its application by assessing chemicals' toxicity to different nematode trophic groups. Results: Free-living nematode populations extracted from soil were exposed to methanol and phenyl isothiocyanate (PEITC). Biospeckle analysis revealed differing behavioural responses as a function of nematode feeding groups. Trichodorus nematodes were less sensitive than were bacterial feeding nematodes or non-trichodorid plant feeding nematodes. Following 24 h of exposure to PEITC, bioactivity significantly decreased for plant and bacterial feeders but not for Trichodorus nematodes. Decreases in movement for plant and bacterial feeders in the presence of PEITC also led to measurable changes to the morphology of biospeckle patterns. Conclusions: Biospeckle analysis can be used to accelerate the screening of nematode bioactivity, thereby providing a fast way of testing the specificity of potential nematicidal compounds. With nematodes' distinctive movement and activity levels being visible in the biospeckle pattern, the technique has potential to screen the behavioural responses of diverse trophic nematode communities. The method discriminates both behavioural responses, morphological traits and activity levels and hence could be used to assess the specificity of nematicidal compounds. [ABSTRACT FROM AUTHOR]

Plant hormones play a vital role in plant immune responses. However, in contrast to the relative wealth of information on hormone-mediated immunity in dicot plants, little information is available on monocot-virus defense systems., We used a high-throughput-sequencing approach to compare the global gene expression of Rice black-streaked dwarf virus ( RBSDV)-infected rice plants with that of healthy plants. Exogenous hormone applications and transgenic rice were used to test RBSDV infectivity and pathogenicity., Our results revealed that the jasmonic acid ( JA) pathway was induced while the brassinosteroid ( BR) pathway was suppressed in infected plants. Foliar application of methyl jasmonate (MeJA) or brassinazole ( BRZ) resulted in a significant reduction in RBSDV incidence, while epibrassinolide ( BL) treatment increased RBSDV infection. Infection studies using coi1-13 and Go mutants demonstrated JA-mediated resistance and BR-mediated susceptibility to RBSDV infection., A mixture of Me JA and BL treatment resulted in a significant reduction in RBSDV infection compared with a single BL treatment. Me JA application efficiently suppressed the expression of BR pathway genes, and this inhibition depended on the JA coreceptor Os COI1. Collectively, our results reveal that JA-mediated defense can suppress the BR-mediated susceptibility to RBSDV infection. [ABSTRACT FROM AUTHOR]