Acidic dileucine motifs in the cylindrical inclusion protein of turnip mosaic virus are crucial for endosomal targeting and viral replication

Construction of watermelon mosaic virus-Beijing isolate infectious clone and study of the dynamic localization and accumulation of virus-encoded proteins

Potyvirus is the largest genus of plant RNA viruses, and the members in the genus are known to cause significant damage to a wide variety of crops. In this study, we performed small RNA (sRNA) deep sequencing for identification of potential virus (es) in collected cucumber leaves with mosaic symptoms from fields in Beijing. Through this high-throughput sequencing and subsequent PCR amplification, we obtained a complete viral genome sequence of 10,044 bp, which showed the highest similarity to the watermelon mosaic virus (WMV) isolate FBR04-37 and exhibited the typical characteristics of potyviruses in its genome organization. The obtained WMV isolate was designated as WMV-BJ. We then constructed the infectious clone of WMV-BJ, which can successfully infect six kinds of cucurbitaceous plants by agroinfiltration. Among these, Cucumis melo showed obvious symptoms such as shrinkage and mosaic compared to other cucurbitaceous plants infected by this virus infectious clone. To understand the biological function of WMV-BJ, we further analyzed the dynamic subcellular localization and protein accumulation of WMV-BJ encoded 11 viral proteins. The results showed the WMV-BJ-encoded proteins displayed diverse subcellular localizations, and most viral proteins were easily degraded after expression in plant cells. Together, the construction of the WMV-BJ infectious clone in this study provides a valuable tool for further exploring the biology of this virus and the interaction between WMV-BJ and host plant, and useful information for investigating the functions of WMV-encoded proteins.

Structural and functional implications of MIT2 and NT2 mutations in amodiaquine and piperaquine resistant Plasmodium berghei parasites

Long-acting drugs, amodiaquine (AQ), lumefantrine (LM), and piperaquine (PQ), are vital components of artemisinin-based combination therapies (ACTs) for malaria treatment. However, the emergence of partial artemisinin-resistant parasites poses significant challenges, particularly in malaria-endemic regions. Despite extensive research, parasite's resistance mechanisms to these drugs still need complete elucidation. This study investigated the genetic basis of resistance to AQ, LM, and PQ using Plasmodium berghei, focusing on selected genes encoding transport proteins in Plasmodium species. In silico bioinformatics tools were used to map genes encoding transport proteins, their ligand-binding sites, and their conservation across different Plasmodium species. PCR amplification and sequence analysis were employed to examine single nucleotide polymorphisms (SNPs) in the genes encoding the selected transporters in AQ, LM, and PQ-resistant P. berghei. The structural impacts of the mutations were evaluated using AlphaFold, ITASSER, UCSF Chimera, and MOTIF Finder. Genes encoding CorA-like Mg2+ transporter protein (MIT2), nucleoside transporter 2 (NT2), ABC Transporter G family member 2 (ABCG2), and novel putative transporter 1 (NPT1) transport proteins with notable conserved motifs and ligand-binding motifs in Plasmodium species were selected and examined. In AQ-resistant (AQR) parasites, a non-synonymous mutation (I433∗) was found in MIT2. PQ-resistant (PQR) parasites possessed a non-synonymous mutation (D511H) in NT2 and a silent mutation in the NPT1 protein. No mutations were observed in the targeted regions of the transporters in LM-resistant (LMR) parasites, nor in the ligand-binding motifs of ABCG2 across all resistant strains. These findings suggest that selection pressure from AQ and PQ leads to mutations in MIT2 and NT2. Further investigation is required to understand how these mutations affect drug susceptibility on a functional level.

FATTY ACID DESATURASE4 enhances plant RNA virus replication and undergoes host vacuolar ATPase-mediated degradation

Emerging evidence indicates that fatty acid (FA) metabolic pathways regulate host immunity to vertebrate viruses. However, information on FA signaling in plant virus infection remains elusive. In this study, we demonstrate the importance of fatty acid desaturase (FAD), an enzyme that catalyzes the rate-limiting step in the conversion of saturated FAs into unsaturated FAs, during infection by a plant RNA virus. We previously found that the rare Kua-ubiquitin-conjugating enzyme (Kua-UEV1) fusion protein FAD4 from Nicotiana benthamiana (NbFAD4) was downregulated upon turnip mosaic virus (TuMV) infection. We now demonstrate that NbFAD4 is unstable and is degraded as TuMV infection progresses. NbFAD4 is required for TuMV replication, as it interacts with TuMV replication protein 6K2 and colocalizes with viral replication complexes. Moreover, NbFAD4 overexpression dampened the accumulation of immunity-related phytohormones and FA metabolites, and its catalytic activity appears to be crucial for TuMV infection. Finally, a yeast 2-hybrid library screen identified the vacuolar H+-ATPase component ATP6V0C as involved in NbFAD4 degradation and further suppression of TuMV infection. This study reveals the intricate role of FAD4 in plant virus infection, and sheds light on a new mechanism by which a V-ATPase is involved in plant antiviral defense.

A sword or a buffet: plant endomembrane system in viral infections

The plant endomembrane system is an elaborate collection of membrane-bound compartments that perform distinct tasks in plant growth and development, and in responses to abiotic and biotic stresses. Most plant viruses are positive-strand RNA viruses that remodel the host endomembrane system to establish intricate replication compartments. Their fundamental role is to create optimal conditions for viral replication, and to protect replication complexes and the cell-to-cell movement machinery from host defenses. In addition to the intracellular antiviral defense, represented mainly by RNA interference and effector-triggered immunity, recent findings indicate that plant antiviral immunity also includes membrane-localized receptor-like kinases that detect viral molecular patterns and trigger immune responses, which are similar to those observed for bacterial and fungal pathogens. Another recently identified part of plant antiviral defenses is executed by selective autophagy that mediates a specific degradation of viral proteins, resulting in an infection arrest. In a perpetual tug-of-war, certain host autophagy components may be exploited by viral proteins to support or protect an effective viral replication. In this review, we present recent advances in the understanding of the molecular interplay between viral components and plant endomembrane-associated pathways.

Proteomics Identified UDP-Glycosyltransferase Family Members as Pro-Viral Factors for Turnip Mosaic Virus Infection in Nicotiana benthamiana

Viruses encounter numerous host factors that facilitate or suppress viral infection. Although some host factors manipulated by viruses were uncovered, we have limited knowledge of the pathways hijacked to promote viral replication and activate host defense responses. Turnip mosaic virus (TuMV) is one of the most prevalent viral pathogens in many regions of the world. Here, we employed an isobaric tag for relative and absolute quantitation (iTRAQ)-based proteomics approach to characterize cellular protein changes in the early stages of infection of Nicotiana benthamiana by wild type and replication-defective TuMV. A total of 225 differentially accumulated proteins (DAPs) were identified (182 increased and 43 decreased). Bioinformatics analysis showed that a few biological pathways were associated with TuMV infection. Four upregulated DAPs belonging to uridine diphosphate-glycosyltransferase (UGT) family members were validated by their mRNA expression profiles and their effects on TuMV infection. NbUGT91C1 or NbUGT74F1 knockdown impaired TuMV replication and increased reactive oxygen species production, whereas overexpression of either promoted TuMV replication. Overall, this comparative proteomics analysis delineates the cellular protein changes during early TuMV infection and provides new insights into the role of UGTs in the context of plant viral infection.

Manipulation of the Cellular Membrane-Cytoskeleton Network for RNA Virus Replication and Movement in Plants

Viruses infect all cellular life forms and cause various diseases and significant economic losses worldwide. The majority of viruses are positive-sense RNA viruses. A common feature of infection by diverse RNA viruses is to induce the formation of altered membrane structures in infected host cells. Indeed, upon entry into host cells, plant-infecting RNA viruses target preferred organelles of the cellular endomembrane system and remodel organellar membranes to form organelle-like structures for virus genome replication, termed as the viral replication organelle (VRO) or the viral replication complex (VRC). Different viruses may recruit different host factors for membrane modifications. These membrane-enclosed virus-induced replication factories provide an optimum, protective microenvironment to concentrate viral and host components for robust viral replication. Although different viruses prefer specific organelles to build VROs, at least some of them have the ability to exploit alternative organellar membranes for replication. Besides being responsible for viral replication, VROs of some viruses can be mobile to reach plasmodesmata (PD) via the endomembrane system, as well as the cytoskeleton machinery. Viral movement protein (MP) and/or MP-associated viral movement complexes also exploit the endomembrane-cytoskeleton network for trafficking to PD where progeny viruses pass through the cell-wall barrier to enter neighboring cells.