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As obligate intracellular parasites, viruses depend on host proteins and pathways for their multiplication. Among these host factors, specific nuclear proteins are involved in the life cycle of some cytoplasmic replicating RNA viruses, although their role in the viral cycle remains largely unknown. The polerovirus turnip yellows virus (TuYV) encodes a major coat protein (CP) and a 74 kDa protein known as the readthrough (RT) protein. The icosahedral viral capsid is composed of the CP and a minor component RT*, arising from a C-terminal cleavage of the full-length RT. In this study, we identified Arabidopsis (Arabidopsis thaliana) ALY family proteins as interacting partners of TuYV structural proteins using yeast 2-hybrid assays and co-immunoprecipitations in planta. ALY proteins are adaptor proteins of the THO-TREX-1 complex essential to the nuclear export of mature messenger RNAs (mRNAs). Although all 4 ALY proteins colocalized with the CP and the RT protein in the nucleus upon co-expression in agro-infiltrated Nicotiana benthamiana leaves, only the CP remained nuclear and colocalized with ALY proteins in TuYV-infected cells, suggesting that the CP is an essential partner of ALY proteins. Importantly, TuYV-infected A. thaliana 4xaly knock-out mutants showed a significant increase in viral accumulation, indicating that TuYV infection is affected by an unknown ALY-mediated antiviral defense mechanism or impairs the cellular mRNA export pathway to favor viral RNA translation. This finding underpins the crucial role played by nuclear factors in the life cycle of cytoplasmic RNA viruses., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

The green peach aphid ( Myzus persicae ) is a generalist pest damaging crops and transmitting viral pathogens. Using Illumina sequencing of small (s)RNAs and poly(A)-enriched long RNAs, we analyzed aphid virome components, viral gene expression and antiviral RNA interference (RNAi) responses. Myzus persicae densovirus (family Parvoviridae ), a single-stranded (ss)DNA virus persisting in the aphid population, produced 22 nucleotide sRNAs from both strands of the entire genome, including 5'- and 3'-inverted terminal repeats. These sRNAs likely represent Dicer-dependent small interfering (si)RNAs, whose double-stranded RNA precursors are produced by readthrough transcription beyond poly(A) signals of the converging leftward and rightward transcription units, mapped here with Illumina reads. Additionally, the densovirus produced 26-28 nucleotide sRNAs, comprising those enriched in 5'-terminal uridine and mostly derived from readthrough transcripts and those enriched in adenosine at position 10 from their 5'-end and mostly derived from viral mRNAs. These sRNAs likely represent PIWI-interacting RNAs generated by a ping-pong mechanism. A novel ssRNA virus, reconstructed from sRNAs and classified into the family Flaviviridae , co-persisted with the densovirus and produced 22 nucleotide siRNAs from the entire genome. Aphids fed on plants versus artificial diets exhibited distinct RNAi responses affecting densovirus transcription and flavivirus subgenomic RNA production. In aphids vectoring turnip yellows virus (family Solemoviridae ), a complete virus genome was reconstituted from 21, 22 and 24 nucleotide viral siRNAs likely acquired with plant phloem sap. Collectively, deep-sequencing analysis allowed for the identification and de novo reconstruction of M. persicae virome components and uncovered RNAi mechanisms regulating viral gene expression and replication.

Many plant viruses modify the phenotype of their hosts, which may influence the behaviour of their vectors and facilitate transmission. Among them is the turnip yellows virus (TuYV), which can modify the orientation, feeding, and performance of its main aphid vector, Myzus persicae. However, the virus factors driving these mechanisms have not been elucidated. In this study, we compared the feeding behaviour and fecundity of aphids on TuYV-infected and transgenic Arabidopsis thaliana expressing individual TuYV proteins (CP, RT and P0) to define the role of these proteins in aphid-plant interactions. Aphids on TuYV-infected plants had shorter pathway phases and ingested phloem sap for longer times, which is expected to promote the acquisition of the phloem-limited TuYV. No change in aphid fecundity was observed on TuYV-infected plants. The transmission-conducive feeding behaviour changes could be fully reproduced by phloem-specific expression of the capsid protein (CP) in transgenic plants, whereas expression of P0 had minor and RT had no effects on aphid feeding behaviour. We then carried out a metabolomic analysis to determine plant compounds that could be involved in the modification of the aphid behaviour. A few metabolites were specific for TuYV-infected or CP-transgenic A. thaliana, and are good candidates for inducing behavioural changes., (© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Multi-infection of plants by viruses is very common and can change drastically infection parameters such as virus accumulation, distribution, and vector transmission. Sugar beet is an important crop that is frequently co-infected by the polerovirus beet chlorosis virus (BChV) and the closterovirus beet yellows virus (BYV), both vectored by the green peach aphid ( Myzus persicae ). These phloem-limited viruses are acquired while aphids ingest phloem sap from infected plants. Here we found that co-infection decreased transmission of BChV by ~50% but had no impact on BYV transmission. The drastic reduction of BChV transmission was due to neither lower accumulation of BChV in co-infected plants nor reduced phloem sap ingestion by aphids from these plants. Using the signal amplification by exchange reaction fluorescent in situ hybridization technique on plants, we observed that 40% of the infected phloem cells were co-infected and that co-infection caused redistribution of BYV in these cells. The BYV accumulation pattern changed from distinct intracellular spherical inclusions in mono-infected cells to a diffuse form in co-infected cells. There, BYV co-localized with BChV throughout the cytoplasm, indicative of virus-virus interactions. We propose that BYV-BChV interactions could restrict BChV access to the sieve tubes and reduce its accessibility for aphids and present a model of how co-infection could alter BChV intracellular movement and/or phloem loading and reduce BChV transmission.IMPORTANCEMixed viral infections in plants are understudied yet can have significant influences on disease dynamics and virus transmission. We investigated how co-infection with two unrelated viruses, BChV and BYV, affects aphid transmission of the viruses in sugar beet plants. We show that co-infection reduced BChV transmission by about 50% without affecting BYV transmission, despite similar virus accumulation rates in co-infected and mono-infected plants. Follow-up experiments examined the localization and intracellular distribution of the viruses, leading to the discovery that co-infection caused a redistribution of BYV in the phloem vessels and altered its repartition pattern within plant cells, suggesting virus-virus interactions. In conclusion, the interplay between BChV and BYV affects the transmission of BChV but not BYV, possibly through direct or indirect virus-virus interactions at the cellular level. Understanding these interactions could be crucial for managing virus propagation in crops and preventing yield losses., Competing Interests: The authors declare no conflict of interest.

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21). DS is a gene dosage disorder that results in multiple phenotypes including congenital heart defects. This clinically important cardiac pathology is the result of a third copy of one or more of the approximately 230 genes on Hsa21, but the identity of the causative dosage-sensitive genes and hence mechanisms underlying this cardiac pathology remain unclear. Here, we show that hearts from human fetuses with DS and embryonic hearts from the Dp1Tyb mouse model of DS show reduced expression of mitochondrial respiration genes and cell proliferation genes. Using systematic genetic mapping, we determined that three copies of the dual-specificity tyrosine phosphorylation-regulated kinase 1A ( Dyrk1a ) gene, encoding a serine/threonine protein kinase, are associated with congenital heart disease pathology. In embryos from Dp1Tyb mice, reducing Dyrk1a gene copy number from three to two reversed defects in cellular proliferation and mitochondrial respiration in cardiomyocytes and rescued heart septation defects. Increased dosage of DYRK1A protein resulted in impairment of mitochondrial function and congenital heart disease pathology in mice with DS, suggesting that DYRK1A may be a useful therapeutic target for treating this common human condition.

Background: Autism spectrum disorders affect more than 1% of the population, impairing social communication and increasing stereotyped behaviours. A micro-deletion of the 16p11.2 BP4-BP5 chromosomic region has been identified in 1% of patients also displaying intellectual disabilities. In mouse models generated to understand the mechanisms of this deletion, learning and memory deficits were pervasive in most genetic backgrounds, while social communication deficits were only detected in some models., Methods: To complement previous studies, we itemized the social deficits in the mouse model of 16p11.2 deletion on a hybrid C57BL/6N × C3H. Pde6b + genetic background. We examined whether behavioural deficits were visible over long-term observation periods lasting several days and nights, to parallel everyday-life assessment of patients. We recorded the individual and social behaviours of mice carrying a heterozygous deletion of the homologous 16p11.2 chromosomic region (hereafter Del/+) and their wild-type littermates from both sexes over two or three consecutive nights during social interactions of familiar mixed-genotype quartets of males and of females, and of same-genotype unfamiliar female pairs., Results: We observed that Del/+ mice of both sexes increased significantly their locomotor activity compared to wild-type littermates. In the social domain, Del/+ mice of both sexes displayed widespread deficits, even more so in males than in females in quartets of familiar individuals. In pairs, significant perturbations of the organisation of the social communication and behaviours appeared in Del/+ females., Discussion: Altogether, this suggests that, over long recording periods, the phenotype of the 16p11.2 Del/+ mice was differently affected in the locomotor activity and the social domains and between the two sexes. These findings confirm the importance of testing models in long-term conditions to provide a comprehensive view of their phenotype that will refine the study of cellular and molecular mechanisms and complement pre-clinical targeted therapeutic trials., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2023 Rusu, Chevalier, de Chaumont, Nalesso, Brault, Hérault and Ey.)

Stefin B (cystatin B) is an inhibitor of lysosomal and nuclear cysteine cathepsins. The gene for stefin B is located on human chromosome 21 and its expression is upregulated in the brains of individuals with Down syndrome. Biallelic loss-of-function mutations in the stefin B gene lead to Unverricht-Lundborg disease-progressive myoclonus epilepsy type 1 (EPM1) in humans. In our past study, we demonstrated that mice lacking stefin B were significantly more sensitive to sepsis induced by lipopolysaccharide (LPS) and secreted higher levels of interleukin 1-β (IL-1β) due to increased inflammasome activation in bone marrow-derived macrophages. Here, we report lower interleukin 1-β processing and caspase-11 expression in bone marrow-derived macrophages prepared from mice that have an additional copy of the stefin B gene. Increased expression of stefin B downregulated mitochondrial reactive oxygen species (ROS) generation and lowered the NLR family pyrin domain containing 3 (NLRP3) inflammasome activation in macrophages. We determined higher AMP-activated kinase phosphorylation and downregulation of mTOR activity in stefin B trisomic macrophages-macrophages with increased stefin B expression. Our study showed that increased stefin B expression downregulated mitochondrial ROS generation and increased autophagy. The present work contributes to a better understanding of the role of stefin B in regulation of autophagy and inflammasome activation in macrophages and could help to develop new treatments.

The success of virus transmission by vectors relies on intricate trophic interactions between three partners, the host plant, the virus, and the vector. Despite numerous studies that showed the capacity of plant viruses to manipulate their host plant to their benefit, and potentially of their transmission, the molecular mechanisms sustaining this phenomenon has not yet been extensively analyzed at the molecular level. In this study, we focused on the deregulations induced in Arabidopsis thaliana by an aphid vector that were alleviated when the plants were infected with turnip yellows virus (TuYV), a polerovirus strictly transmitted by aphids in a circulative and nonpropagative mode. By setting up an experimental design mimicking the natural conditions of virus transmission, we analyzed the deregulations in plants infected with TuYV and infested with aphids by a dual transcriptomic and metabolomic approach. We observed that the virus infection alleviated most of the gene deregulations induced by the aphids in a noninfected plant at both time points analyzed (6 and 72 h) with a more pronounced effect at the later time point of infestation. The metabolic composition of the infected and infested plants was altered in a way that could be beneficial for the vector and the virus transmission. Importantly, these substantial modifications observed in infected and infested plants correlated with a higher TuYV transmission efficiency. This study revealed the capacity of TuYV to alter the plant nutritive content and the defense reaction against the aphid vector to promote the viral transmission., Competing Interests: The author(s) declare no conflict of interest.

We used the NanoLuc luciferase bioluminescent reporter system to detect turnip yellows virus (TuYV) in infected plants. For this, TuYV was genetically tagged by replacing the C-terminal part of the RT protein with full-length NanoLuc (TuYV-NL) or with the N-terminal domain of split NanoLuc (TuYV-N65-NL). Wild-type and recombinant viruses were agro-infiltrated in Nicotiana benthamiana , Montia perfoliata , and Arabidopsis thaliana . ELISA confirmed systemic infection and similar accumulation of the recombinant viruses in N. benthamiana and M. perfoliata but reduced systemic infection and lower accumulation in A. thaliana . RT-PCR analysis indicated that the recombinant sequences were stable in N. benthamiana and M. perfoliata but not in A. thaliana . Bioluminescence imaging detected TuYV-NL in inoculated and systemically infected leaves. For the detection of split NanoLuc, we constructed transgenic N. benthamiana plants expressing the C-terminal domain of split NanoLuc. Bioluminescence imaging of these plants after agro-infiltration with TuYV-N65-NL allowed the detection of the virus in systemically infected leaves. Taken together, our results show that NanoLuc luciferase can be used to monitor infection with TuYV.

Evidence is accumulating that plant viruses alter host plant traits in ways that modify their insect vectors' behavior. These alterations often enhance virus transmission, which has led to the hypothesis that these effects are manipulations caused by viral adaptation. However, we lack a mechanistic understanding of the genetic basis of these indirect, plant-mediated effects on vectors, their dependence on the plant host, and their relation to the mode of virus transmission. Transcriptome profiling of Arabidopsis thaliana and Camelina sativa plants infected with turnip yellows virus (TuYV) or cauliflower mosaic virus (CaMV) and infested with the common aphid vector Myzus persicae revealed strong virus- and host-specific differences in gene expression patterns. CaMV infection caused more severe effects on the phenotype of both plant hosts than did TuYV infection, and the severity of symptoms correlated strongly with the proportion of differentially expressed genes, especially photosynthesis genes. Accordingly, CaMV infection modified aphid behavior and fecundity more strongly than did infection with TuYV. Overall, infection with CaMV, relying on the noncirculative transmission mode, tends to have effects on metabolic pathways, with strong potential implications for insect vector-plant host interactions (e.g., photosynthesis, jasmonic acid, ethylene, and glucosinolate biosynthetic processes), while TuYV, using the circulative transmission mode, alters these pathways only weakly. These virus-induced deregulations of genes that are related to plant physiology and defense responses might impact both aphid probing and feeding behavior on infected host plants, with potentially distinct effects on virus transmission. IMPORTANCE Plant viruses change the phenotype of their plant hosts. Some of the changes impact interactions of the plant with insects that feed on the plants and transmit these viruses. These modifications may result in better virus transmission. We examine here the transcriptomes of two plant species infected with two viruses with different transmission modes to work out whether there are plant species-specific and transmission mode-specific transcriptome changes. Our results show that both are the case.

Background: Poleroviruses, such as turnip yellows virus (TuYV), are plant viruses strictly transmitted by aphids in a persistent and circulative manner. Acquisition of either virus particles or plant material altered by virus infection is expected to induce gene expression deregulation in aphids which may ultimately alter their behavior., Results: By conducting an RNA-Seq analysis on viruliferous aphids fed either on TuYV-infected plants or on an artificial medium containing purified virus particles, we identified several hundreds of genes deregulated in Myzus persicae, despite non-replication of the virus in the vector. Only a few genes linked to receptor activities and/or vesicular transport were common between the two modes of acquisition with, however, a low level of deregulation. Behavioral studies on aphids after virus acquisition showed that M. persicae locomotion behavior was affected by feeding on TuYV-infected plants, but not by feeding on the artificial medium containing the purified virus particles. Consistent with this, genes potentially involved in aphid behavior were deregulated in aphids fed on infected plants, but not on the artificial medium., Conclusions: These data show that TuYV particles acquisition alone is associated with a moderate deregulation of a few genes, while higher gene deregulation is associated with aphid ingestion of phloem from TuYV-infected plants. Our data are also in favor of a major role of infected plant components on aphid behavior., (© 2022. The Author(s).)