Ubiquitin-Conjugating Enzyme E2 E Inhibits the Accumulation of Rice Stripe Virus in Laodelphax striatellus (Fallén)

Polyubiquitylated rice stripe virus NS3 translocates to the nucleus to promote cytosolic virus replication via miRNA-induced fibrillin 2 upregulation

Viruses are encapsidated mobile genetic elements that rely on host cells for replication. Several cytoplasmic RNA viruses synthesize proteins and/or RNAs that translocate to infected cell nuclei. However, the underlying mechanisms and role(s) of cytoplasmic-nuclear trafficking are unclear. We demonstrate that infection of small brown planthoppers with rice stripe virus (RSV), a negarnaviricot RNA virus, results in K63-linked polyubiquitylation of RSV's nonstructural protein 3 (NS3) at residue K127 by the RING ubiquitin ligase (E3) LsRING. In turn, ubiquitylation leads to NS3 trafficking from the cytoplasm to the nucleus, where NS3 regulates primary miRNA pri-miR-92 processing through manipulation of the microprocessor complex, resulting in accumulation of upregulated miRNA lst-miR-92. We show that lst-miR-92 regulates the expression of fibrillin 2, an extracellular matrix protein, thereby increasing RSV loads. Our results highlight the manipulation of intranuclear, cytoplasmic, and extracellular components by an RNA virus to promote its own replication in an insect vector.

Differential Expression of miRNAs Involved in Response to Candidatus Liberibacter asiaticus Infection in Mexican Lime at Early and Late Stages of Huanglongbing Disease

Huanglongbing (HLB) is one of the most destructive diseases threatening citriculture worldwide. This disease has been associated with α-proteobacteria species, namely Candidatus Liberibacter. Due to the unculturable nature of the causal agent, it has been difficult to mitigate the disease, and nowadays a cure is not available. MicroRNAs (miRNAs) are key regulators of gene expression, playing an essential role in abiotic and biotic stress in plants including antibacterial responses. However, knowledge derived from non-model systems including Candidatus Liberibacter asiaticus (CLas)-citrus pathosystem remains largely unknown. In this study, small RNA profiles from Mexican lime (Citrus aurantifolia) plants infected with CLas at asymptomatic and symptomatic stages were generated by sRNA-Seq, and miRNAs were obtained with ShortStack software. A total of 46 miRNAs, including 29 known miRNAs and 17 novel miRNAs, were identified in Mexican lime. Among them, six miRNAs were deregulated in the asymptomatic stage, highlighting the up regulation of two new miRNAs. Meanwhile, eight miRNAs were differentially expressed in the symptomatic stage of the disease. The target genes of miRNAs were related to protein modification, transcription factors, and enzyme-coding genes. Our results provide new insights into miRNA-mediated regulation in C. aurantifolia in response to CLas infection. This information will be useful to understand molecular mechanisms behind the defense and pathogenesis of HLB.

Voltage-dependent anion channel 2 (VDAC2) facilitates the accumulation of rice stripe virus in the vector Laodelphax striatellus

Rice stripe virus (RSV) causes enormous losses in rice production and is transmitted by the small brown planthopper, Laodelphax striatellus, in a persistent-propagative manner. RSV accumulation within the gut lumen of the vector is indispensable for the successful transmission to rice and insects. In this study, we obtained a 1464 bp full-length cDNA of a voltage-dependent anion channel 2 from L. striatellus (LsVDAC2), which encodes a 283 amino acid protein. RSV infection increased the expression of LsVDAC2 in the midguts and ovaries of L. striatellus by 260% and 228%, respectively. Silencing of LsVDAC2 resulted in a 88% reduction of RSV loads at 24 h after RNAi, indicating that LsVDAC2 facilitates RSV accumulation in the vector. Yeast two-hybrid and GST pulldown assays demonstrated that LsVDAC2 interacted with RSV RNA-dependent RNA polymerase, RdRp. Furthermore, experiments in vivo and in vitro showed that LsVDAC2 induced the apoptotic response in RSV-infected insects and tissues. Silencing of LsVDAC2 via RNAi significantly reduced the expression of genes for apoptosis-related caspases 1a and 1c by 62% and 78%, respectively, in RSV-infected vectors. Whether LsVDAC2-induced RSV accumulation is related to RSV RdRp and LsVDAC2-induced cell apoptosis deserves further investigation.

Comprehensive Analysis of Ubiquitome Changes in Nicotiana benthamiana after Rice Stripe Virus Infection

Rice stripe virus (RSV) is one of the most devastating viruses affecting rice production. During virus infection, ubiquitination plays an important role in the dynamic regulation of host defenses. We combined the ubiquitomics approach with the label-free quantitation proteomics approach to investigate potential ubiquitination status changes of Nicotiana benthamiana infected with RSV. Bioinformatics analyses were performed to elucidate potential associations between proteins with differentially ubiquitinated sites (DUSs) and various cellular components/pathways during virus infection. In total, 399 DUSs in 313 proteins were identified and quantified, among them 244 ubiquitinated lysine (Kub) sites in 186 proteins were up-regulated and 155 Kub sites in 127 proteins were down-regulated at 10 days after RSV infection. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses indicated that proteins with up-regulated Kub sites were significantly enriched in the ribosome. Silencing of 3-isopropylmalate dehydratase large subunit through virus-induced gene silencing delayed RSV infection, while silencing of mRNA-decapping enzyme-like protein promoted RSV symptom in the late stage of infection. Moreover, ubiquitination was observed in all seven RSV-encoded proteins. Our study supplied the comprehensive analysis of the ubiquitination changes in N. benthamiana after RSV infection, which is helpful for understanding RSV pathogenesis and RSV-host interactions.

Silencing suppressors of rice black-streaked dwarf virus and rice stripe virus hijack the 26S proteasome of Laodelphax striatellus to facilitate virus accumulation and transmission

BACKGROUND

Rice black-streaked dwarf virus (RBSDV) is transmitted by small brown planthopper (Laodelphax striatellus [L. striatellus]) and causes devastating disease in rice. P9-1 has silencing suppression activity and is the key protein for viroplasm formation in RBSDV-infected plants and insects; however, its exact function is poorly understood.

RESULTS

In this study, the P9-1 of RBSDV interacted with L. striatellus 26S proteasome subunit RPN8. RBSDV accumulation in L. striatellus increased after the 26S proteasome was disrupted by silencing the RPN8 expression. This finding indicated that L. striatellus 26S proteasome played a defense role against RBSDV infection by regulating RBSDV accumulation. Further investigations revealed that P9-1 could competitively bind to RPN8 with RPN7, thereby disrupting the assembly of 26S proteasome in L. striatellus and promoting the infection of RBSDV in insect vectors, and further affecting the transmission of the virus to rice by insect vectors. Similar to P9-1, rice stripe virus (RSV) NS2, a weak silencing suppressor, regulated virus accumulation and transmission by hijacking RPN8 to interfere with the function of 26S proteasome in L. striatellus.

CONCLUSION

These results suggest that viruses promote their own infection via interfering with ubiquitination pathway of insect vectors, and this mechanism might be of universal importance. These findings provide a new insight into the mechanism of virus transmission in insect vectors. © 2022 Society of Chemical Industry.

Rice stripe virus: Exploring Molecular Weapons in the Arsenal of a Negative-Sense RNA Virus

Rice stripe disease caused by Rice stripe virus (RSV) is one of the most devastating plant viruses of rice and causes enormous losses in production. RSV is transmitted from plant to plant by the small brown planthopper (Laodelphax striatellus) in a circulative-propagative manner. The recent reemergence of this pathogen in East Asia since 2000 has made RSV one of the most studied plant viruses over the past two decades. Extensive studies of RSV have resulted in substantial advances regarding fundamental aspects of the virus infection. Here, we compile and analyze recent information on RSV with a special emphasis on the strategies that RSV has adopted to establish infections. These advances include RSV replication and movement in host plants and the small brown planthopper vector, innate immunity defenses against RSV infection, epidemiology, and recent advances in the management of rice stripe disease. Understanding these issues will facilitate the design of novel antiviral therapies for management and contribute to a more detailed understanding of negative-sense virus-host interactions at the molecular level.

The Bunyavirales: The Plant-Infecting Counterparts

Negative-strand (-) RNA viruses (NSVs) comprise a large and diverse group of viruses that are generally divided in those with non-segmented and those with segmented genomes. Whereas most NSVs infect animals and humans, the smaller group of the plant-infecting counterparts is expanding, with many causing devastating diseases worldwide, affecting a large number of major bulk and high-value food crops. In 2018, the taxonomy of segmented NSVs faced a major reorganization with the establishment of the order Bunyavirales. This article overviews the major plant viruses that are part of the order, i.e., orthospoviruses (Tospoviridae), tenuiviruses (Phenuiviridae), and emaraviruses (Fimoviridae), and provides updates on the more recent ongoing research. Features shared with the animal-infecting counterparts are mentioned, however, special attention is given to their adaptation to plant hosts and vector transmission, including intra/intercellular trafficking and viral counter defense to antiviral RNAi.