Prediction and experimental confirmation of banana bract mosaic virus encoding miRNAs and their targets

Small Talk: On the Possible Role of Trans-Kingdom Small RNAs during Plant-Virus-Vector Tritrophic Communication

Small RNAs (sRNAs) are the hallmark and main effectors of RNA silencing and therefore are involved in major biological processes in plants, such as regulation of gene expression, antiviral defense, and plant genome integrity. The mechanisms of sRNA amplification as well as their mobile nature and rapid generation suggest sRNAs as potential key modulators of intercellular and interspecies communication in plant-pathogen-pest interactions. Plant endogenous sRNAs can act in cis to regulate plant innate immunity against pathogens, or in trans to silence pathogens' messenger RNAs (mRNAs) and impair virulence. Likewise, pathogen-derived sRNAs can act in cis to regulate expression of their own genes and increase virulence towards a plant host, or in trans to silence plant mRNAs and interfere with host defense. In plant viral diseases, virus infection alters the composition and abundance of sRNAs in plant cells, not only by triggering and interfering with the plant RNA silencing antiviral response, which accumulates virus-derived small interfering RNAs (vsiRNAs), but also by modulating plant endogenous sRNAs. Here, we review the current knowledge on the nature and activity of virus-responsive sRNAs during virus-plant interactions and discuss their role in trans-kingdom modulation of virus vectors for the benefit of virus dissemination.

High throughput sRNA sequencing revealed gene regulatory role mediated by pathogen-derived small RNAs during Sri Lankan Cassava Mosaic Virus infection in Cassava

Small RNA (sRNA) mediated gene regulation during Sri Lankan Cassava Mosaic Virus (SLCMV) infection was studied from the Indian Cassava Cultivar H226. Our study generated high throughput sRNA dataset of 23.64 million reads from the control and SLCMV infected H226 leaf libraries. mes-miR9386 was detected as the most prominent miRNA expressed in control and infected leaf. Among the differentially expressed miRNAs, mes-miR156, mes- miR395 and mes-miR535a/b showed significant down regulation in the infected leaf. Genome-wide analysis of the three small RNA profiles revealed critical role of virus-derived small RNAs (vsRNAs) from the infected leaf tissues of H226. The vsRNAs were mapped to the bipartite SLCMV genome and high expression of siRNAs generated from the virus genomic region encoding AV1/AV2 genes in the infected leaf pointed towards the susceptibility of H226 cultivars to SLCMV. Furthermore, the sRNA reads mapped to the antisense strand of the SLCMV ORFs was higher than the sense strand. These vsRNAs were potential to target key host genes involved in virus interaction such as aldehyde dehydrogenase, ADP-ribosylation factor1 and ARF1-like GTP-binding proteins. The sRNAome-assisted analysis also revealed the origin of virus-encoded miRNAs from the SLCMV genome in the infected leaf. These virus-derived miRNAs were predicted to have hair-pin like secondary structures, and have different isoforms. Moreover, our study revealed that the pathogen sRNAs play a critical role in the infection process in H226 plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03494-2.

Exploring diverse roles of micro RNAs in banana: Current status and future prospective

Micro RNAs (miRNAs) are 20-24 nucleotides long non-coding RNA sequences identified and characterized in multiple plant and animal systems. miRNAs play multifarious roles ranging from plant development to stress tolerance by synchronizing physiological processes at the level of transcription and translation. Banana is a major horticultural crop with colossal production worldwide. Despite the recent encouraging developments, the information on functions of miRNAs in banana plants is still in its infancy. The available literature pertaining to miRNAs in banana plants hints towards their contribution as master regulators in crucial physiological processes for instance abiotic stress responses, pathogenic defence response, fruit ripening and so on. This review is focused on biogenesis of miRNAs, their identification and deciphering their respective roles in banana plants with special emphasis on abiotic stress responses, plant immune responses, fruit ripening and storage. Based on the prior reports, we identified a few miRNAs with prospective roles in stress tolerance and illustrated the potential applications of miRNAs in banana crop improvement utilizing recent biotechnological tools such as CRISPR cas9, RNAi and the nano particle based foliar spray of miRNAs. The review briefly explained the future directions in banana research with a special emphasis on miRNA regulatory networks and agronomic traits improvement. Finally, future domains in miRNA research in plants and their possible applications towards crop improvement in agriculture are described briefly.

The potential use of microRNAs as a therapeutic strategy for SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To date, there is no effective therapeutic approach for treating SARS-CoV-2 infections. MicroRNAs (miRNAs) have been recognized to target the viral genome directly or indirectly, thereby inhibiting viral replication. Several studies have demonstrated that host miRNAs target different sites in SARS-CoV-2 RNA and constrain the production of essential viral proteins. Furthermore, miRNAs have lower toxicity, are more immunogenic, and are more diverse than protein-based and even plasmid-DNA-based therapeutic agents. In this review, we emphasize the role of miRNAs in viral infection and their potential use as therapeutic agents against COVID-19 disease. The potential of novel miRNA delivery strategies, especially EDV™ nanocells, for targeting lung tissue for treatment of SARS-CoV-2 infection is also discussed.

Comparative study of potyvirid NIa proteases and their cleavage sites

Nuclear inclusion a protease (NIaPro), a major protease of potyvirids, processes its cognate viral polyprotein at distinct cleavage sites. Although Potyviridae is the largest family of the realm Riboviria, the individual NIaPro enzymes and their cleavage sites are believed to be species-specific. In the present study, the NIaPro amino acid sequences of 165 potyvirids of 10 genera and their 1154 cleavage sites were compared to understand their genus/species-specificity and functional regulation. Of these, the NIaPro of macluraviruses, maintains a constant length of 217 amino acids, while those of other genera allow variation. In particular, poaceviruses exhibited a broad range of NIaPro amino acid sequence lengths. Alignment of 162 NIaPro amino acid sequences showed that the N- and C-terminal regions allow variations, while the central region, with the catalytic triad and S1 subsite, are highly conserved. NIaPro cleavage sites are composed of seven amino acids (heptapeptide) denoted as P6-P5-P4-P3-P2-P1/P1'. A survey of 1154 cleavage sites showed that the P1 position is predominantly occupied by Gln/Glu, as is seen in picornaviruses. The P6 (Glu), P4 (Val/Cys/Gln), P2 (His/Tyr/Leu), and P1' (Ser/Ala/Gly/Met) positions are predominantly occupied by genus-specific residues, while P5 and P3 are not genus-specific. The 6K2-VPg and VPg-NIaPro junctions possess Glu at the P1 position in order to maintain latency.

Virus and Viroid-Derived Small RNAs as Modulators of Host Gene Expression: Molecular Insights Into Pathogenesis

Virus-derived siRNAs (vsiRNAs) generated by the host RNA silencing mechanism are effectors of plant’s defense response and act by targeting the viral RNA and DNA in post-transcriptional gene silencing (PTGS) and transcriptional gene silencing (TGS) pathways, respectively. Contrarily, viral suppressors of RNA silencing (VSRs) compromise the host RNA silencing pathways and also cause disease-associated symptoms. In this backdrop, reports describing the modulation of plant gene(s) expression by vsiRNAs via sequence complementarity between viral small RNAs (sRNAs) and host mRNAs have emerged. In some cases, silencing of host mRNAs by vsiRNAs has been implicated to cause characteristic symptoms of the viral diseases. Similarly, viroid infection results in generation of sRNAs, originating from viroid genomic RNAs, that potentially target host mRNAs causing typical disease-associated symptoms. Pathogen-derived sRNAs have been demonstrated to have the propensity to target wide range of genes including host defense-related genes, genes involved in flowering and reproductive pathways. Recent evidence indicates that vsiRNAs inhibit host RNA silencing to promote viral infection by acting as decoy sRNAs. Nevertheless, it remains unclear if the silencing of host transcripts by viral genome-derived sRNAs are inadvertent effects due to fortuitous pairing between vsiRNA and host mRNA or the result of genuine counter-defense strategy employed by viruses to enhance its survival inside the plant cell. In this review, we analyze the instances of such cross reaction between pathogen-derived vsiRNAs and host mRNAs and discuss the molecular insights regarding the process of pathogenesis.