Roles of small RNAs in the establishment of tolerant interaction between plants and viruses

Plant virology: an RNA treasure trove

Key principles pertaining to RNA biology not infrequently have their origins in plant virology. Examples have arisen from studies on viral RNA-intrinsic properties and the infection process from gene expression, replication, movement, and defense evasion to biotechnological applications. Since RNA is at the core of the central dogma in molecular biology, how plant virology assisted in the reinforcement or adaptations of this concept, while at other instances shook up elements of the doctrine, is discussed. Moreover, despite the negative effects of viral diseases in agriculture worldwide, plant viruses can be considered a scientific treasure trove. Today they remain tools of discovery for biotechnology, studying evolution, cell biology, and host-microbe interactions.

A bioinformatic approach of targeting SARS-CoV-2 replication by silencing a conserved alternative reserve of the orf8 gene using host miRNAs

The causative agent of the COVID-19 pandemic, the SARS-CoV-2 virus has yielded multiple relevant mutations, many of which have branched into major variants. The Omicron variant has a huge similarity with the original viral strain (first COVID-19 strain from Wuhan). Among different genes, the highly variable orf8 gene is responsible for crucial host interactions and has undergone multiple mutations and indels. The sequence of the orf8 gene of the Omicron variant is, however, identical with the gene sequence of the wild type. orf8 modulates the host immunity making it easier for the virus to conceal itself and remain undetected. Variants seem to be deleting this gene without affecting the viral replication. While analyzing, we came across the conserved orf7a gene in the viral genome which exhibits a partial sequence homology as well as functional similarity with the SARS-CoV-2 orf8. Hence, we have proposed here in our hypothesis that, orf7a might be an alternative reserve of orf8 present in the virus which was compensating for the lost gene. A computational approach was adopted where we screened various miRNAs targeted against the orf8 gene. These miRNAs were then docked onto the orf8 mRNA sequences. The same set of miRNAs was then used to check for their binding affinity with the orf7a reference mRNA. Results showed that miRNAs targeting the orf8 had favorable shape complementarity and successfully docked with the orf7a gene as well. These findings provide a basis for developing new therapeutic approaches where both orf8 and orf7a can be targeted simultaneously.

Transcriptome and Small RNA Profiling of Potato Virus Y Infected Potato Cultivars, Including Systemically Infected Russet Burbank

Potatoes are the world’s most produced non-grain crops and an important food source for billions of people. Potatoes are susceptible to numerous pathogens that reduce yield, including Potato virus Y (PVY). Genetic resistance to PVY is a sustainable way to limit yield and quality losses due to PVY infection. Potato cultivars vary in their susceptibility to PVY and include susceptible varieties such as Russet Burbank, and resistant varieties such as Payette Russet. Although the loci and genes associated with PVY-resistance have been identified, the genes and mechanisms involved in limiting PVY during the development of systemic infections have yet to be fully elucidated. To increase our understanding of PVY infection, potato antiviral responses, and resistance, we utilized RNA sequencing to characterize the transcriptomes of two potato cultivars. Since transcriptional responses associated with the extreme resistance response occur soon after PVY contact, we analyzed the transcriptome and small RNA profile of both the PVY-resistant Payette Russet cultivar and PVY-susceptible Russet Burbank cultivar 24 h post-inoculation. While hundreds of genes, including terpene synthase and protein kinase encoding genes, exhibited increased expression, the majority, including numerous genes involved in plant pathogen interactions, were downregulated. To gain greater understanding of the transcriptional changes that occur during the development of systemic PVY-infection, we analyzed Russet Burbank leaf samples one week and four weeks post-inoculation and identified similarities and differences, including higher expression of genes involved in chloroplast function, photosynthesis, and secondary metabolite production, and lower expression of defense response genes at those time points. Small RNA sequencing identified different populations of 21- and 24-nucleotide RNAs and revealed that the miRNA profiles in PVY-infected Russet Burbank plants were similar to those observed in other PVY-tolerant cultivars and that during systemic infection ~32% of the NLR-type disease resistance genes were targeted by 21-nt small RNAs. Analysis of alternative splicing in PVY-infected potato plants identified splice variants of several hundred genes, including isoforms that were more dominant in PVY-infected plants. The description of the PVYN-Wi-associated transcriptome and small RNA profiles of two potato cultivars described herein adds to the body of knowledge regarding differential outcomes of infection for specific PVY strain and host cultivar pairs, which will help further understanding of the mechanisms governing genetic resistance and/or virus-limiting responses in potato plants.

OUP accepted manuscript

Potyviridae, the largest family of known RNA viruses (realm Riboviria), belongs to the picorna-like supergroup and has important agricultural and ecological impacts. Potyvirid genomes are translated into polyproteins, which are in turn hydrolyzed to release mature products. Recent sequencing efforts revealed an unprecedented number of potyvirids with a rich variability in gene content and genomic layouts. Here, we review the heterogeneity of non-core modules that expand the structural and functional diversity of the potyvirid proteomes. We provide a family-wide classification of P1 proteinases into the functional Types A and B, and discuss pretty interesting sweet potato potyviral ORF (PISPO), putative zinc fingers, and alkylation B (AlkB)—non-core modules found within P1 cistrons. The atypical inosine triphosphate pyrophosphatase (ITPase/HAM1), as well as the pseudo tobacco mosaic virus-like coat protein (TMV-like CP) are discussed alongside homologs of unrelated virus taxa. Family-wide abundance of the multitasking helper component proteinase (HC-pro) is revised. Functional connections between non-core modules are highlighted to support host niche adaptation and immune evasion as main drivers of the Potyviridae evolutionary radiation. Potential biotechnological and synthetic biology applications of potyvirid leader proteinases and non-core modules are finally explored.

Genotoxic Evaluation of Fe3O4 Nanoparticles in Different Three Barley (Hordeum vulgare L.) Genotypes to Explore the Stress-Resistant Molecules

Sustainable agricultural practices are still essential due to soil degradation and crop losses. Recently, the relationship between plants and nanoparticles (NPs) attracted scientists’ attention, especially for applications in agricultural production as nanonutrition. Therefore, the present research was carried out to investigate the effect of Fe₃O₄ NPs at low concentrations (0, 1, 10, and 20 mg/L) on three genotypes of barley (Hordeum vulgare L.) seedlings grown in hydroponic conditions. Significant increases in seedling growth, enhanced chlorophyll quality and quantity, and two miRNA expression levels were observed. Additionally, increased genotoxicity was observed in seedlings grown with NPs. Generally, Fe₃O₄ NPs at low concentrations could be successfully used as nanonutrition for increasing barley photosynthetic efficiency with consequently enhanced yield. These results are important for a better understanding of the potential impact of Fe₃O₄ NPs at low concentrations in agricultural crops and the potential of these NPs as nanonutrition for barley growth and yield enhancement. Future studies are needed to investigate the effect of these NPs on the expression of resistance-related genes and chlorophyll synthesis-related gene expression in treated barley seedlings.

Trigger and Suppression of Antiviral Defenses by Grapevine Pinot Gris Virus (GPGV): Novel Insights into Virus-Host Interaction

Grapevine Pinot gris virus (GPGV) is an emerging trichovirus that has been putatively associated with a novel grapevine disease known as grapevine leaf mottling and deformation (GLMD). Yet the role of GPGV in GLMD disease is poorly understood, since it has been detected both in symptomatic and symptomless grapevines. We exploited a recently constructed GPGV infectious clone (pRI::GPGV-vir) to induce an antiviral response in Nicotiana benthamiana plants. In silico prediction of virus-derived small interfering RNAs and gene expression analyses revealed the involvement of DCL4, AGO5, and RDR6 genes during GPGV infection, suggesting the activation of the posttranscriptional gene-silencing (PTGS) pathway as a plant antiviral defense. PTGS suppression assays in transgenic N. benthamiana 16c plants revealed the ability of the GPGV coat protein to suppress RNA silencing. This work provides novel insights on the interaction between GPGV and its host, revealing the ability of the virus to trigger and suppress antiviral RNA silencing.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

miRNAs; a novel strategy for the treatment of COVID-19

Coronavirus disease 2019 (COVID‐19) is the seventh member of the bat severe acute respiratory syndrome family. COVID‐19 can fuse their envelopes with the host cell membranes and deliver their genetic material. COVID‐19 attacks the respiratory system and stimulates the host inflammatory responses, enhances the recruitment of immune cells, and promotes angiotensin‐converting enzyme 2 activities. Patients with confirmed COVID‐19 may have experienced fever, dry cough, headache, dyspnea, acute kidney injury, acute respiratory distress syndrome, and acute heart injury. Several strategies such as oxygen therapy, ventilation, antibiotic or antiviral therapy, and renal replacement therapy are commonly used to decrease COVID‐19‐associated mortality. However, these approaches may not be good treatment options. Therefore, the search for an alternative‐novel therapy is urgently important to prevent the disease progression. Recently, microRNAs (miRNAs) have emerged as a promising strategy for COVID‐19. The design of oligonucleotide against the genetic material of COVID‐19 might suppress virus RNA translation. Several previous studies have shown that host miRNAs play an antiviral role and improve the treatment of patients with COVID‐19. miRNAs by binding to the 3′‐untranslated region (UTR) or 5′‐UTR of viral RNA play an important role in COVID‐19‐host interplay and viral replication. miRNAs interact with multiple pathways and reduce inflammatory biomarkers, thrombi formation, and tissue damage to accelerate the patient outcome. The information in this review provides a summary of the current clinical application of miRNAs for the treatments of patients with COVID‐19.

The role of miRNA in plant-virus interaction: a review

Plant viruses affect crop production both quantitatively and qualitatively. The viral genome consists of either DNA or RNA. However, most plant viruses are positive single-strand RNA viruses. MicroRNAs are involved in gene regulation and affect development as well as host-virus interaction. They are non-coding short with 20-24 nucleotides long capable of regulating gene expression. The miRNA gene is transcribed by RNA polymerase II to form pri-miRNA which will later cleaved by Dicer-like 1 to produce pre-miRNA with the help of HYPONASTIC LEAVES1 and SERRATE which finally methylated and exported via nucleopore with the help of HASTY. The outcome of plant virus interaction depends on the effectiveness of host defense and the ability of a virus counter-defense mechanism. In plants, miRNAs are involved in the repression of gene expression through transcript cleavage. On the other hand, viruses use viral suppressors of RNA silencing (VSRs) which affect RISC assembly and subsequent mRNA degradation. Passenger strands, miRNA*, have a significant biological function in plant defense response as well as plant development.

Recent advances in understanding plant antiviral RNAi and viral suppressors of RNAi

Molecular plant-virus interactions provide an excellent model to understanding host antiviral immunity and viral counter-defense mechanisms. The primary antiviral defense is triggered inside the infected plant cell by virus-derived small-interfering RNAs, which guide homology-dependent RNA interference (RNAi) and/or RNA-directed DNA methylation (RdDM) to target RNA and DNA viruses. In counter-defense, plant viruses have independently evolved viral suppressors of RNAi (VSRs) to specifically antagonize antiviral RNAi. Recent studies have shown that plant antiviral responses are regulated by endogenous small silencing RNAs, RNA decay and autophagy and that some known VSRs of plant RNA and DNA viruses also target these newly recognized defense responses to promote infection. This review focuses on these recent advances that have revealed multilayered regulation of plant-virus interactions.