Mutational analysis of Aedes aegypti Dicer 2 provides insights into the biogenesis of antiviral exogenous small interfering RNAs.

The exogenous small interfering RNA (exo-siRNA) pathway is a key antiviral mechanism in the Aedes aegypti mosquito, a widely distributed vector of human-pathogenic arboviruses. This pathway is induced by virus-derived double-stranded RNAs (dsRNA) that are cleaved by the ribonuclease Dicer 2 (Dcr2) into predominantly 21 nucleotide (nt) virus-derived small interfering RNAs (vsiRNAs). These vsiRNAs are used by the effector protein Argonaute 2 within the RNA-induced silencing complex to cleave target viral RNA. Dcr2 contains several domains crucial for its activities, including helicase and RNase III domains. In Drosophila melanogaster Dcr2, the helicase domain has been associated with binding to dsRNA with blunt-ended termini and a processive siRNA production mechanism, while the platform-PAZ domains bind dsRNA with 3' overhangs and subsequent distributive siRNA production. Here we analyzed the contributions of the helicase and RNase III domains in Ae. aegypti Dcr2 to antiviral activity and to the exo-siRNA pathway. Conserved amino acids in the helicase and RNase III domains were identified to investigate Dcr2 antiviral activity in an Ae. aegypti-derived Dcr2 knockout cell line by reporter assays and infection with mosquito-borne Semliki Forest virus (Togaviridae, Alphavirus). Functionally relevant amino acids were found to be conserved in haplotype Dcr2 sequences from field-derived Ae. aegypti across different continents. The helicase and RNase III domains were critical for silencing activity and 21 nt vsiRNA production, with RNase III domain activity alone determined to be insufficient for antiviral activity. Analysis of 21 nt vsiRNA sequences (produced by functional Dcr2) to assess the distribution and phasing along the viral genome revealed diverse yet highly consistent vsiRNA pools, with predominantly short or long sequence overlaps including 19 nt overlaps (the latter representing most likely true Dcr2 cleavage products). Combined with the importance of the Dcr2 helicase domain, this suggests that the majority of 21 nt vsiRNAs originate by processive cleavage. This study sheds new light on Ae. aegypti Dcr2 functions and properties in this important arbovirus vector species.

Atypical molecular features of RNA silencing against the phloem-restricted polerovirus TuYV.

In plants and some animal lineages, RNA silencing is an efficient and adaptable defense mechanism against viruses. To counter it, viruses encode suppressor proteins that interfere with RNA silencing. Phloem-restricted viruses are spreading at an alarming rate and cause substantial reduction of crop yield, but how they interact with their hosts at the molecular level is still insufficiently understood. Here, we investigate the antiviral response against phloem-restricted turnip yellows virus (TuYV) in the model plant Arabidopsis thaliana. Using a combination of genetics, deep sequencing, and mechanical vasculature enrichment, we show that the main axis of silencing active against TuYV involves 22-nt vsiRNA production by DCL2, and their preferential loading into AGO1. Moreover, we identify vascular secondary siRNA produced from plant transcripts and initiated by DCL2-processed AGO1-loaded vsiRNA. Unexpectedly, and despite the viral encoded VSR P0 previously shown to mediate degradation of AGO proteins, vascular AGO1 undergoes specific post-translational stabilization during TuYV infection. Collectively, our work uncovers the complexity of antiviral RNA silencing against phloem-restricted TuYV and prompts a re-assessment of the role of its suppressor of silencing P0 during genuine infection.

A truncated intracellular Dicer-like molecule involves in antiviral immune recognition of oyster Crassostrea gigas.

The enzyme Dicer is best known for its role as an endoribonuclease in the small RNA pathway, playing a crucial role in recognizing viral double-stranded RNA (dsRNA) and inducing down-stream cascades to mediate anti-virus immunity. In the present study, a truncated Dicer-like gene was identified from oyster Crassostrea gigas, and its open reading frame (ORF) encoded a polypeptide (designed as CgDCL) of 530 amino acids. The CgDCL contained one N-terminal DEAD domain and a C-terminal helicase domain, but lack the conserved PAZ domain, ribonuclease domain (RIBOc) and dsRNA binding domain. The mRNA transcripts of CgDCL were detected in all the examined tissues with high expression levels in lip, gills and haemocytes, which were 62.06-fold, 48.91-fold and 47.13-fold (p < 0.05) of that in mantle, respectively. In the primarily cultured oyster haemocytes, the mRNA transcripts of CgDCL were significantly induced at 12 h after poly(I:C) stimulation, which were 4.04-fold (p < 0.05) of that in control group. The expression level of CgDCL mRNA in haemocytes was up-regulated significantly after dsRNA and recombinant interferon-like protein (rCgIFNLP) injection, which was 12.87-fold (p < 0.01) and 3.22-fold (p < 0.05) of that in control group, respectively. CgDCL proteins were mainly distributed in the cytoplasm of haemocytes. The recombinant CgDCL protein displayed binding activity to dsRNA and poly(I:C), but no obvious dsRNA cleavage activity. These results collectively suggest that truncated CgDCL from C. gigas was able to be activated by poly(I:C), dsRNA and CgIFNLP, and functioned as an intracellular recognition molecule to bind nucleic acid of virus, indicating a potential mutual cooperation between RNAi and IFN-like system in anti-virus immunity of oysters.

Gain-of-"endocytic' function in mutant p53 cancer cells.

Beyond its well-known canonical function as a tumor suppressor, p53 is also involved in numerous cellular processes through altered transcription under both normal and pathological conditions. The functional diversity of p53 outputs is complex and dependent on cell context. However, the underlying mechanisms responsible for this diversity remain largely unclear. The emerging evidence of p53 mutations involved in regulating endocytic trafficking and signaling, in tandem to promote malignancy (invasion, exosome biogenesis and immune evasion), sheds light on possible mechanisms behind the p53-driven complexity. The interrelated nature of endocytic trafficking and receptor signaling that form dynamic and adaptable feedback loops - either positive or negative - functions to modulate multiple cellular outputs. Biasing the tunable endocytic trafficking and receptor signaling network by mutant p53 expands the purview of p53, allowing its contribution to diverse and aggressive phenotypes. In this review, we explore recent studies in which the novel role of mutant p53 in altering endocytic trafficking to bias receptor signaling and drive transforming phenotypes is revealed. Understanding the complex crosstalk of mutant p53, endocytic trafficking and receptor signaling will allow the development of therapies to selectively target p53-altered endocytic processes.

The Dicer from oyster Crassostrea gigas functions as an intracellular recognition molecule and effector in anti-viral immunity.

Dicer, as a member of ribonuclease III family, functions in RNA interference (RNAi) pathway to direct sequence-specific degradation of cognate mRNA. It plays important roles in antiviral immunity and production of microRNAs. In the present study, a Dicer gene was identified from oyster Crassostrea gigas, and its open reading frame (ORF) encoded a polypeptide (designed as CgDicer) of 1873 amino acids containing two conserved ribonuclease III domains (RIBOc) and a double-stranded RNA-binding motif (DSRM). The deduced amino acid sequence of CgDicer shared identities ranging from 18.5% to 46.6% with that of other identified Dicers. The mRNA transcripts of CgDicer were detectable in all the examined tissues of adult oysters, with the highest expression in hemocytes (11.21 ±â€¯1.64 fold of that in mantle, p < 0.05). The mRNA expression level of CgDicer in hemocytes was significantly up-regulated (36.70 ±â€¯11.10 fold, p < 0.01) after the oysters were treated with double-stranded RNA (dsRNA). In the primarily cultured oyster hemocytes, the mRNA transcripts of CgDicer were significantly induced at 12 h after the stimulation with poly(I:C), which were 2.04-fold (p < 0.05) higher than that in control group. Immunocytochemistry assay revealed that CgDicer proteins were mainly distributed in the cytoplasm of hemocytes. The two most important functional domains of CgDicer, DSRM and RIBOc, were recombinant expressed in Escherichia coli transetta (DE3), and the recombinant DSRM protein displayed significantly binding activity to dsRNA and poly(I:C) in vitro, while the recombinant RIBOc protein exhibited significantly dsRNase activity to cleave dsRNA in vitro. These results collectively suggested that CgDicer functioned as either an intracellular recognition molecule to bind dsRNA or an effector with ribonuclease activity, which might play a crucial role in anti-viral immunity of oyster.

Signal Transduction in Human Cell Lysate via Dynamic RNA Nanotechnology.

Dynamic RNA nanotechnology with small conditional RNAs (scRNAs) offers a promising conceptual approach to introducing synthetic regulatory links into endogenous biological circuits. Here, we use human cell lysate containing functional Dicer and RNases as a testbed for engineering scRNAs for conditional RNA interference (RNAi). scRNAs perform signal transduction via conditional shape change: detection of a subsequence of mRNA input X triggers formation of a Dicer substrate that is processed to yield small interfering RNA (siRNA) output anti-Y targeting independent mRNA Y for destruction. Automated sequence design is performed using the reaction pathway designer within NUPACK to encode this conditional hybridization cascade into the scRNA sequence subject to the sequence constraints imposed by X and Y. Because it is difficult for secondary structure models to predict which subsequences of mRNA input X will be accessible for detection, here we develop the RNAhyb method to experimentally determine accessible windows within the mRNA that are provided to the designer as sequence constraints. We demonstrate the programmability of scRNA regulators by engineering scRNAs for transducing in both directions between two full-length mRNAs X and Y, corresponding to either the forward molecular logic "if X then not Y" (X [Formula: see text] Y) or the reverse molecular logic "if Y then not X" (Y [Formula: see text] X). In human cell lysate, we observe a strong OFF/ON conditional response with low crosstalk, corresponding to a ≈20-fold increase in production of the siRNA output in response to the cognate versus noncognate full-length mRNA input. 2'OMe-RNA chemical modifications protect signal transduction reactants and intermediates against RNase degradation while enabling Dicer processing of signal transduction products. Because diverse biological pathways interact with RNA, scRNAs that transduce between detection of endogenous RNA inputs and production of biologically active RNA outputs hold great promise as a synthetic regulatory paradigm.

Dicer-2 Regulates Resistance and Maintains Homeostasis against Zika Virus Infection in Drosophila.

Zika virus (ZIKV) outbreaks pose a massive public health threat in several countries. We have developed an in vivo model to investigate the host-ZIKV interaction in Drosophila We have found that a strain of ZIKV replicates in wild-type flies without reducing their survival ability. We have shown that ZIKV infection triggers RNA interference and that mutating Dicer-2 results in enhanced ZIKV load and increased susceptibility to ZIKV infection. Using a flavivirus-specific Ab, we have found that ZIKV is localized in the gut and fat body cells of the infected wild-type flies and results in their perturbed homeostasis. In addition, Dicer-2 mutants display severely reduced insulin activity, which could contribute toward the increased mortality of these flies. Our work establishes the suitability of Drosophila as the model system to study host-ZIKV dynamics, which is expected to greatly advance our understanding of the molecular and physiological processes that determine the outcome of this disease.

Immune priming and clearance of orally acquired RNA viruses in Drosophila.

Immune responses in insects are differentially triggered depending on the infection route used by the pathogen. In most studies involving Drosophila melanogaster and viruses, infection is done by injection, while oral infection, which is probably the most common route of viral entry in nature, remains unexplored. Here, we orally infected adults and larvae from wild-type and RNA interference (RNAi) mutant flies with different RNA viruses. We found that, in contrast with what is observed following virus injection, oral infections initiated at larval or adult stages are cleared in adult flies. Virus elimination occurred despite a larger infectious dose than for injected flies and evidence of viral replication. RNAi mutant flies suffered greater mortality relative to wild-type flies following oral infection, but they also eliminated the virus, implying that RNAi is not essential for viral clearance and that other immune mechanisms act during oral infections. We further showed that information of infection by RNA viruses acquired orally leaves a trace under a DNA form, which confers protection against future reinfection by the same virus. Together, this work presents evidence of clearance and immune priming for RNA viruses in insects and challenges the current view of antiviral immunity in insects.

Small interfering RNA pathway contributes to antiviral immunity in Spodoptera frugiperda (Sf9) cells following Autographa californica multiple nucleopolyhedrovirus infection.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is a well-known virus in the Baculoviridae family. Presence of the p35 gene in the AcMNPV genome as a suppressor of the short interfering RNA (siRNA) pathway is a strong reason for the importance of the siRNA pathway in the host cellular defense. Given that, here we explored the roles of Dicer-2 (Dcr2) and Argonaute 2 (Ago2) genes, key factors in the siRNA pathway in response to AcMNPV infection in Spodoptera frugiperda Sf9 cells. The results showed that the transcript levels of Dcr2 and Ago2 increased in response to AcMNPV infection particularly over 16 h post infection suggesting induction of the siRNA pathway. Reductions in the expression levels of Dcr2 and Ago2 by using specific dsRNAs in Sf9 cells modestly enhanced production of viral genomic DNA which indicated their role in the host antiviral defense. Using deep sequencing, our previous study showed a large number of small reads (siRNAs of ∼20 nucleotides) from AcMNPV-infected Sf9 cells that were mapped to some of the viral genes (hot spots). Down-regulation of Dcr2 in Sf9 cells resulted in enhanced expression levels of the selected virus hotspot genes (i.e. ORF-9 and ORF-148), while the transcript levels of virus cold spots (i.e. ORF-18 and ORF-25) with no or few siRNAs mapped to them did not change. Overexpression of AcMNPV p35 as a suppressor of RNAi and anti-apoptosis gene in Sf9 cells increased virus replication. Also, replication of mutant AcMNPV lacking the p35 gene was significantly increased in Sf9 cells with reduced transcript levels of Dcr2 and Ago2, highlighting the antiviral role of the siRNA pathway in Sf9 cells. Together, our results demonstrate that Dcr2 and Ago2 genes contribute in efficient antiviral response of Sf9 cells towards AcMNPV, and in turn, the AcMNPV p35 suppresses the siRNA pathway, besides being an antiapoptotic protein.

Insights into RNAi-based antiviral immunity in Lepidoptera: acute and persistent infections in Bombyx mori and Trichoplusia ni cell lines.

The control of viral infections in insects is a current issue of major concern and RNA interference (RNAi) is considered the main antiviral immune response in this group of animals. Here we demonstrate that overexpression of key RNAi factors can help to protect insect cells against viral infections. In particular, we show that overexpression of Dicer2 and Argonaute2 in lepidopteran cells leads to improved defense against the acute infection of the Cricket Paralysis Virus (CrPV). We also demonstrate an important role of RNAi in the control of persistent viral infections, as the one caused by the Macula-like Latent Virus (MLV). Specifically, a direct interaction between Argonaute2 and virus-specific small RNAs is shown. Yet, while knocking down Dicer2 and Argonaute2 resulted in higher transcript levels of the persistently infecting MLV in the lepidopteran cells under investigation, overexpression of these proteins could not further reduce these levels. Taken together, our data provide deep insight into the RNAi-based interactions between insects and their viruses. In addition, our results suggest the potential use of an RNAi gain-of-function approach as an alternative strategy to obtain reduced viral-induced mortality in Lepidoptera, an insect order that encompasses multiple species of relevant economic value.

Which Plant Proteins Are Involved in Antiviral Defense? Review on In Vivo and In Vitro Activities of Selected Plant Proteins against Viruses.

Plants have evolved a variety of defense mechanisms to tackle virus attack. Endogenous plant proteins can function as virus suppressors. Different types of proteins mediate defense responses against plant viruses. Pathogenesis-related (PR) proteins are activated upon pathogen infections or in different stress situations and their production is one of many components in plant defense. Ribosome-inactivating proteins (RIPs) suppress translation by enzymatically damaging ribosomes and they have been found to have antiviral activity. RNA-binding proteins (RBPs) bind to target RNAs via specialized RNA-binding domain and can directly or indirectly function in plant defense system against RNA viruses. Proteins involved in silencing machinery, namely Dicer-like (DCL) proteins, Argonaute (AGO) proteins, and RNA-dependent RNA polymerases (RDRs) confer innate antiviral defense in plants as they are able to degrade foreign RNA of viral origin. This review aims to provide a comprehensive and up-to-date picture of plant proteins participating in antiviral defense. As a result we discuss proteins conferring plant antiviral resistance and their potential future applications in different fields of life including agriculture and medicine.

PACT is required for MDA5-mediated immunoresponses triggered by Cardiovirus infection via interaction with LGP2.

Laboratory of genetics and physiology 2 (LGP2) and melanoma differentiation-associated gene 5 (MDA5) cooperatively detect viral RNA in the cytoplasm of Cardiovirus-infected cells and activate innate immune responses. Here, we evaluated whether the double-stranded RNA-binding protein PACT plays a role in this anti-viral response to further elucidate the mechanism. Immunoprecipitation experiments demonstrated that PACT interacts with LGP2 and that this interaction is enhanced by encephalomyocarditis virus (EMCV) infection. In vitro interaction analyses using purified recombinant proteins confirmed that the single-stranded Theiler's murine encephalitis virus genome enhanced the interaction between LGP2 and PACT. Small interfering RNA knockdown experiments further indicated that PACT is required for Cardiovirus-triggered interferon responses. To support this functional interaction with LGP2, overexpressed PACT was shown to enhance EMCV-triggered interferon promoter activity only when LGP2 and MDA5 were co-expressed but not when MDA5 is expressed alone. Together, our findings indicate a possible role of PACT in regulating the Cardiovirus-triggered immune responses mediated by MDA5 and LGP2, which opens the door to novel therapeutic strategies in interferon-related autoimmune diseases and cancer.

Enhanced Reactive Oxygen Species Production, Acidic Cytosolic pH and Upregulated Na+/H+ Exchanger (NHE) in Dicer Deficient CD4+ T Cells.

BACKGROUND: MicroRNAs (miRNAs) negatively regulate gene expression at a post-transcriptional level. Dicer, a cytoplasmic RNase III enzyme, is required for the maturation of miRNAs from precursor miRNAs. Dicer, therefore, is a critical enzyme involved in the biogenesis and processing of miRNAs. Several biological processes are controlled by miRNAs, including the regulation of T cell development and function. T cells generate reactive oxygen species (ROS) with parallel H+ extrusion accomplished by the Na+/H+-exchanger 1 (NHE1). The present study explored whether ROS production, as well as NHE1 expression and function are sensitive to the lack of Dicer (miRNAs deficient) and could be modified by individual miRNAs. METHODS: CD4+ T cells were isolated from CD4 specific Dicer deficient (DicerΔ/Δ) mice and the respective control mice (Dicerfl/fl). Transcript and protein levels were quantified with RT-PCR and Western blotting, respectively. For determination of intracellular pH (pHi) cells were incubated with the pH sensitive dye bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) and Na+/H+ exchanger (NHE) activity was calculated from re-alkalinization after an ammonium pulse. Changes in cell volume were measured using the forward scatter in flow cytometry, and ROS production utilizing 2',7' -dichlorofluorescin diacetate (DCFDA) fluorescence. Transfection of miRNA-control and mimics in T cells was performed using DharmaFECT3 reagent. RESULTS: ROS production, cytosolic H+ concentration, NHE1 transcript and protein levels, NHE activity, and cell volume were all significantly higher in CD4+ T cells from DicerΔ/Δ mice than in CD4+ T cells from Dicerfl/fl mice. Furthermore, individual miR-200b and miR-15b modify pHi and NHE activity in Dicerfl/fl and DicerΔ/Δ CD4+ T cells, respectively. CONCLUSIONS: Lack of Dicer leads to oxidative stress, cytosolic acidification, upregulated NHE1 expression and activity as well as swelling of CD4+ T cells, functions all reversed by miR-15b or miR-200b.

Dysregulation of microRNA biogenesis in the small intestine after ethanol and burn injury.

Ethanol exposure at the time of burn injury is a major contributor to post-burn pathogenesis. Many of the adverse effects associated with ethanol and burn injury are linked to an impaired intestinal barrier. The combined insult causes intestinal inflammation, resulting in tissue damage, altered tight junction expression, and increased intestinal permeability. MicroRNAs play a critical role in maintaining intestinal homeostasis including intestinal inflammation and barrier function. Specifically, miR-150 regulates inflammatory mediators which can contribute to gut barrier disruption. The present study examined whether ethanol and burn injury alter expression of microRNA processing enzymes (Drosha, Dicer, and Argonaute-2) and miR-150 in the small intestine. Male mice were gavaged with ethanol (~2.9g/kg) 4h prior to receiving a ~12.5% total body surface area full thickness burn. One or three days after injury, mice were euthanized and small intestinal epithelial cells (IECs) were isolated and analyzed for expression of microRNA biogenesis components and miR-150. Dicer mRNA and protein levels were not changed following the combined insult. Drosha and Argonaute-2 mRNA and protein levels were significantly reduced in IECs one day after injury; which accompanied reduced miR-150 expression. To further determine the role of miR-150 in intestinal inflammation, young adult mouse colonocytes were transfected with a miR-150 plasmid and stimulated with LPS (100ng/ml). miR-150 overexpression significantly reduced IL-6 and KC protein levels compared to vector control cells challenged with LPS. These results suggest that altered microRNA biogenesis and associated decrease in miR-150 likely contribute to increased intestinal inflammation following ethanol and burn injury.

The modulation of Dicer regulates tumor immunogenicity in melanoma.

MicroRNAs (miRs) are small non-coding RNAs that regulate most cellular protein networks by targeting mRNAs for translational inhibition or degradation. Dicer, a type III endoribonuclease, is a critical component in microRNA biogenesis and is required for mature microRNA production. Abnormal Dicer expression occurs in numerous cancer types and correlates with poor patient prognosis. For example, increased Dicer expression in melanoma is associated with more aggressive tumors (higher tumor mitotic index and depth of invasion) and poor patient prognosis. However, the role that Dicer plays in melanoma development and immune evasion remains unclear. Here, we report on a newly discovered relationship between Dicer expression and tumor immunogenicity. To investigate Dicer's role in regulating melanoma immunogenicity, Dicer knockdown studies were performed. We found that B16F0-Dicer deficient cells exhibited decreased tumor growth compared to control cells and were capable of inducing anti-tumor immunity. The decrease in tumor growth was abrogated in immunodeficient NSG mice and was shown to be dependent upon CD8+ T cells. Dicer knockdown also induced a more responsive immune gene profile in melanoma cells. Further studies demonstrated that CD8+ T cells preferentially killed Dicer knockdown tumor cells compared to control cells. Taken together, we present evidence which links Dicer expression to tumor immunogenicity in melanoma.

Dicer expression in estrogen receptor-positive versus triple-negative breast cancer: an antibody comparison.

Dicer is an RNase III enzyme responsible for cleaving double-stranded RNAs into small interfering RNAs and microRNAs, which either target messenger RNA transcripts for degradation or inhibit translation. Dicer protein levels have been examined in breast cancer with contradictory results. Our goal was to resolve whether Dicer levels differ in breast cancer versus normal breast epithelium and between estrogen receptor-α-positive (ER+) or estrogen receptor-α-negative (ER-) primary breast cancers. We compared 3 different Dicer antibodies: Abcam 4A6, Abcam ab5818, and Sigma HPA000694, using immunohistochemistry and Western blot analyses. All 3 Dicer antibodies detected higher levels of Dicer in ER+ breast cancer cell lines versus ER-, and all 3 recognized exogenous overexpressed Dicer. In clinical specimens, all 3 antibodies detected higher Dicer in ER+ breast cancers versus triple-negative breast cancer (TNBC) but had very different staining patterns by immunohistochemistry on the same tumor samples. Using the optimal antibody, ab5818, selected for its sensitivity and specificity, Dicer protein expression was significantly higher in ER+ versus TNBC clinical specimens of primary tumor (P<.0001, unpaired t test). Dicer was also significantly higher in adjacent normal breast epithelium versus TNBC (P<.0001, paired t test; n=18 pairs). Differences in antibody performance may explain contrasting results observed in the literature regarding Dicer protein in breast cancer. If Dicer becomes more clinically relevant as a prognostic indicator, further antibody optimization and standardization will be critical.

Rewiring macrophages for anti-tumour immunity.

Tumour-associated macrophages facilitate cancer progression, but whether they can be reprogrammed to elicit an anti-tumour response remains unclear. Deletion of the microRNA-processing enzyme Dicer is now shown to rewire macrophages to an anti-tumour mode, leading to an enhanced response to immunotherapy and inhibition of tumour progression.

Gene Expression Analysis of Plum pox virus (Sharka) Susceptibility/Resistance in Apricot (Prunus armeniaca L.).

RNA-Seq has proven to be a very powerful tool in the analysis of the Plum pox virus (PPV, sharka disease)/Prunus interaction. This technique is an important complementary tool to other means of studying genomics. In this work an analysis of gene expression of resistance/susceptibility to PPV in apricot is performed. RNA-Seq has been applied to analyse the gene expression changes induced by PPV infection in leaves from two full-sib apricot genotypes, "Rojo Pasión" and "Z506-7", resistant and susceptible to PPV, respectively. Transcriptomic analyses revealed the existence of more than 2,000 genes related to the pathogen response and resistance to PPV in apricot. These results showed that the response to infection by the virus in the susceptible genotype is associated with an induction of genes involved in pathogen resistance such as the allene oxide synthase, S-adenosylmethionine synthetase 2 and the major MLP-like protein 423. Over-expression of the Dicer protein 2a may indicate the suppression of a gene silencing mechanism of the plant by PPV HCPro and P1 PPV proteins. On the other hand, there were 164 genes involved in resistance mechanisms that have been identified in apricot, 49 of which are located in the PPVres region (scaffold 1 positions from 8,050,804 to 8,244,925), which is responsible for PPV resistance in apricot. Among these genes in apricot there are several MATH domain-containing genes, although other genes inside (Pleiotropic drug resistance 9 gene) or outside (CAP, Cysteine-rich secretory proteins, Antigen 5 and Pathogenesis-related 1 protein; and LEA, Late embryogenesis abundant protein) PPVres region could also be involved in the resistance.