Molecular dialogues between viruses and receptor-like kinases in plants

Two viral proteins translated from one open reading frame target different layers of plant defense

Multilayered defense responses are activated upon pathogen attack. Viruses utilize a number of strategies to maximize the coding capacity of their small genomes and produce viral proteins for infection, including suppression of host defense. Here, we reveal translation leakage as one of these strategies: two viral effectors encoded by tomato golden mosaic virus, chloroplast-localized C4 (cC4) and membrane-associated C4 (mC4), are translated from two in-frame start codons and function cooperatively to suppress defense. cC4 localizes in chloroplasts, to which it recruits NbPUB4 to induce ubiquitination of the outer membrane; as a result, this organelle is degraded, and chloroplast-mediated defenses are abrogated. However, chloroplast-localized cC4 induces the production of singlet oxygen (1O2), which in turn promotes translocation of the 1O2 sensor NbMBS1 from the cytosol to the nucleus, where it activates expression of the CERK1 gene. Importantly, an antiviral effect exerted by CERK1 is countered by mC4, localized at the plasma membrane. mC4, like cC4, recruits NbPUB4 and promotes the ubiquitination and subsequent degradation of CERK1, suppressing membrane-based, receptor-like kinase-dependent defenses. Importantly, this translation leakage strategy seems to be conserved in multiple viral species and is related to host range. This finding suggests that stacking of different cellular antiviral responses could be an effective way to abrogate viral infection and engineer sustainable resistance to major crop viral diseases in the field.

PSTVd infection in Nicotiana benthamiana plants has a minor yet detectable effect on CG methylation

Viroids are small circular RNAs infecting a wide range of plants. They do not code for any protein or peptide and therefore rely on their structure for their biological cycle. Observed phenotypes of viroid infected plants are thought to occur through changes at the transcriptional/translational level of the host. A mechanism involved in such changes is RNA-directed DNA methylation (RdDM). Till today, there are contradictory works about viroids interference of RdDM. In this study, we investigated the epigenetic effect of viroid infection in Nicotiana benthamiana plants. Using potato spindle tuber viroid (PSTVd) as the triggering pathogen and via bioinformatic analyses, we identified endogenous gene promoters and transposable elements targeted by 24 nt host siRNAs that differentially accumulated in PSTVd-infected and healthy plants. The methylation status of these targets was evaluated following digestion with methylation-sensitive restriction enzymes coupled with PCR amplification, and bisulfite sequencing. In addition, we used Methylation Sensitive Amplification Polymorphism (MSAP) followed by sequencing (MSAP-seq) to study genomic DNA methylation of 5-methylcytosine (5mC) in CG sites upon viroid infection. In this study we identified a limited number of target loci differentially methylated upon PSTVd infection. These results enhance our understanding of the epigenetic host changes as a result of pospiviroid infection.

A novel soybean malectin-like receptor kinase-encoding gene, GmMLRK1, provides resistance to soybean mosaic virus

Soybean mosaic virus (SMV) severely damages soybean [Glycine max (L.) Merr.] yield and seed quality. Moreover, the underlying genetic determinants of resistance to SMV remain largely unknown. Here, we performed a genome-wide association study (GWAS) of SMV resistance in a panel of 219 diverse soybean accessions across four environments and identified a new resistance-related gene, GmMLRK1, at the major resistance locus Rsv4 on chromosome 2. GmMLRK1 encodes a malectin-like receptor kinase (RK) that was induced earlier and to a greater degree in leaves of the SMV-resistant cultivar Kefeng No. 1 than in those of the susceptible cultivar Nannong 1138-2 after inoculation. We demonstrated that soybean plants overexpressing GmMLRK1 show broad-spectrum resistance to both strains SC7 and SC3 on the basis of reduced viral accumulation, increased reactive oxygen species production, and local cell death associated with the hypersensitive response. In contrast, GmMLRK1 knockout mutants were more susceptible to both pathotypes. Haplotype analysis revealed the presence of five haplotypes (H1-H5) within the soybean population, and only H1 provided SMV resistance, which was independent of its tightly linked SMV resistance gene RNase-H at the same locus. These results report a novel gene that adds new understanding of SMV resistance and can be used for breeding resistant soybean accessions.

Genome-wide identification and expression analysis of wall-associated kinase (WAK) and WAK-like kinase gene family in response to tomato yellow leaf curl virus infection in Nicotiana benthamiana

BACKGROUND

Tomato yellow leaf curl virus (TYLCV) is a major monopartite virus in the family Geminiviridae and has caused severe yield losses in tomato and tobacco planting areas worldwide. Wall-associated kinases (WAKs) and WAK-like kinases (WAKLs) are a subfamily of the receptor-like kinase family implicated in cell wall signaling and transmitting extracellular signals to the cytoplasm, thereby regulating plant growth and development and resistance to abiotic and biotic stresses. Recently, many studies on WAK/WAKL family genes have been performed in various plants under different stresses; however, identification and functional survey of the WAK/WAKL gene family of Nicotiana benthamiana have not yet been performed, even though its genome has been sequenced for several years. Therefore, in this study, we aimed to identify the WAK/WAKL gene family in N. benthamiana and explore their possible functions in response to TYLCV infection.

RESULTS

Thirty-eight putative WAK/WAKL genes were identified and named according to their locations in N. benthamiana. Phylogenetic analysis showed that NbWAK/WAKLs are clustered into five groups. The protein motifs and gene structure compositions of NbWAK/WAKLs appear to be highly conserved among the phylogenetic groups. Numerous cis-acting elements involved in phytohormone and/or stress responses were detected in the promoter regions of NbWAK/WAKLs. Moreover, gene expression analysis revealed that most of the NbWAK/WAKLs are expressed in at least one of the examined tissues, suggesting their possible roles in regulating the growth and development of plants. Virus-induced gene silencing and quantitative PCR analyses demonstrated that NbWAK/WAKLs are implicated in regulating the response of N. benthamiana to TYLCV, ten of which were dramatically upregulated in locally or systemically infected leaves of N. benthamiana following TYLCV infection.

CONCLUSIONS

Our study lays an essential base for the further exploration of the potential functions of NbWAK/WAKLs in plant growth and development and response to viral infections in N. benthamiana.

Structural and biochemical basis of Arabidopsis FERONIA receptor kinase-mediated early signaling initiation

Accumulating evidence indicates that early and essential events for receptor-like kinase (RLK) function involve both autophosphorylation and substrate phosphorylation. However, the structural and biochemical basis for these events is largely unclear. Here, we used RLK FERONIA (FER) as a model and crystallized its core kinase domain (FER-KD) and two FER-KD mutants (K565R, S525A) in complexes with ATP/ADP and Mg²⁺ in the unphosphorylated state. Unphosphorylated FER-KD was found to adopt an unexpected active conformation in its crystal structure. Moreover, unphosphorylated FER-KD mutants with reduced (S525A) or no catalytic activity (K565R) also adopt similar active conformations. Biochemical studies revealed that FER-KD is a dual-specificity kinase, and its autophosphorylation is accomplished via an intermolecular mechanism. Further investigations confirmed that initiating substrate phosphorylation requires autophosphorylation of the activation segment on T696, S701, and Y704. This study reveals the structural and biochemical basis for the activation and regulatory mechanism of FER, providing a paradigm for the early steps in RLK signaling initiation.

Whole-Genome Resequencing Deciphers New Insight Into Genetic Diversity and Signatures of Resistance in Cultivated Cotton Gossypium hirsutum

Cotton is an important crop that produces fiber and cottonseed oil for the textile and oil industry. However, cotton leaf curl virus disease (CLCuD) stress is limiting its yield in several Asian countries. In this study, we have sequenced Mac7 accession, a Gossypium hirsutum resistance source against several biotic stresses. By aligning with the Gossypium hirsutum (AD1) 'TM-1' genome, a total of 4.7 and 1.2 million SNPs and InDels were identified in the Mac7 genome. The gene ontology and metabolic pathway enrichment indicated SNPs and InDels role in nucleotide bindings, secondary metabolite synthesis, and plant-pathogen interaction pathways. Furthermore, the RNA-seq data in different tissues and qPCR expression profiling under CLCuD provided individual gene roles in resistant and susceptible accessions. Interestingly, the differential NLR genes demonstrated higher expression in resistant plants rather than in susceptible plants expression. The current resequencing results may provide primary data to identify DNA resistance markers which will be helpful in marker-assisted breeding for development of Mac7-derived resistance lines.

The P3N-PIPO Protein Encoded by Wheat Yellow Mosaic Virus Is a Pathogenicity Determinant and Promotes Its Pathogenicity through Interaction with NbRLK6 in Nicotiana benthamiana

Similarly to other potyvirids, the bymovirus wheat yellow mosaic virus (WYMV) encodes a P3N-PIPO protein that is expressed by frameshifting occurring within the open reading frame of the P3 protein. P3N-PIPO is known to be essential for the cell-to-cell movement of several potyviruses, but this has not yet been confirmed for the WYMV. Here, we show that the WYMV P3N-PIPO protein influences disease symptom formation. Infection of Nicotiana benthamiana plants with a potato virus X (PVX)-based vector carrying the WYMV P3N-PIPO gene induced more severe disease symptoms and resulted in higher virus accumulation levels than did infection with PVX lacking the P3N-PIPO gene. N. benthamiana P3N-PIPO-interacting proteins were identified through co-immunoprecipitation (Co-IP) coupled with LC-MS/MS (mass spectrometry), and the interaction between P3N-PIPO and the N. benthamiana receptor-like kinase NbRLK6 was further verified by Co-IP and bimolecular fluorescence complementation (BiFC) of transiently-expressed proteins. Furthermore, our investigation showed that the disease symptom severity and accumulation level of PVX-P3N-PIPO were decreased in N. benthamiana plants when NbRLK6 expression was reduced by tobacco rattle virus-induced gene silencing.

Tomato zonate spot virus induced hypersensitive resistance via an auxin-related pathway in pepper

Tomato zonate spotvirus (TZSV) often incurs significant losses in many food and ornamental crops in Yunnan province, China, and the surrounding areas. The pepper (Capsicum chinensePI152225)can develop hypersensitive resistance following infection with TZSV, through an as yet unknown mechanism. The transcriptome dataset showed a total of 45.81 GB of clean data were obtained from six libraries, and the average percentage of the reads mapped to the pepper genome was over 90.00 %. A total of 1403 differentially expressed genes (DEGs) were obtained after TZSV infection, including 825significantly up-regulated genes and 578 down-regulated genes. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that most up-regulated DEGs were involved in basal defenses. RT-qPCR, and virus induced gene silencing (VIGS) were used preliminarily to identifyBBC_22506 and BBC_18917, among total of 71 differentially expressed genes (DEGs), that play a key role in mediating the auxin-induced signaling pathway that might take part in hypersensitive response (HR) conferred resistance to viral infection in pepper (PI152225) byTZSV. This is the first study on the mechanism of auxin resistance, involved in defense responses of pepper against viral diseases, which lay the foundation for further study on the pathogenic mechanism of TZSV, as well as the mechanism of resistance to TZSV, in peppers.

The tomato yellow leaf curl virus C4 protein alters the expression of plant developmental genes correlating to leaf upward cupping phenotype in tomato

Tomato yellow leaf curl virus (TYLCV), a monopartite begomovirus in the family Geminiviridae, is efficiently transmitted by the whitefly, Bemisia tabaci, and causes serious economic losses to tomato crops around the world. TYLCV-infected tomato plants develop distinctive symptoms of yellowing and leaf upward cupping. In recent years, excellent progress has been made in the characterization of TYLCV C4 protein function as a pathogenicity determinant in experimental plants, including Nicotiana benthamiana and Arabidopsis thaliana. However, the molecular mechanism leading to disease symptom development in the natural host plant, tomato, has yet to be characterized. The aim of the current study was to generate transgenic tomato plants expressing the TYLCV C4 gene and evaluate differential gene expression through comparative transcriptome analysis between the transgenic C4 plants and the transgenic green fluorescent protein (Gfp) gene control plants. Transgenic tomato plants expressing TYLCV C4 developed phenotypes, including leaf upward cupping and yellowing, that are similar to the disease symptoms expressed on tomato plants infected with TYLCV. In a total of 241 differentially expressed genes identified in the transcriptome analysis, a series of plant development-related genes, including transcription factors, glutaredoxins, protein kinases, R-genes and microRNA target genes, were significantly altered. These results provide further evidence to support the important function of the C4 protein in begomovirus pathogenicity. These transgenic tomato plants could serve as basic genetic materials for further characterization of plant receptors that are interacting with the TYLCV C4.

A fungal protease named AsES triggers antiviral immune responses and effectively restricts virus infection in arabidopsis and Nicotiana benthamiana plants

BACKGROUND AND AIMS

Plants have evolved complex mechanisms to fight against pathogens. Among these mechanisms, pattern-triggered immunity (PTI) relies on the recognition of conserved microbe- or pathogen-associated molecular patterns (MAMPs or PAMPs, respectively) by membrane-bound receptors. Indeed, PTI restricts virus infection in plants and, in addition, BRI1-associated kinase 1 (BAK1), a central regulator of PTI, plays a role in antiviral resistance. However, the compounds that trigger antiviral defences, along with their molecular mechanisms of action, remain mostly elusive. Herein, we explore the role of a fungal extracellular subtilase named AsES in its capacity to trigger antiviral responses.

METHODS

In this study, we obtained AsES by recombinant expression, and evaluated and characterized its capacity to trigger antiviral responses against Tobacco mosaic virus (TMV) by performing time course experiments, analysing gene expression, virus movement and callose deposition.

KEY RESULTS

The results of this study provide direct evidence that exogenous treatment with recombinant AsES increases a state of resistance against TMV infection, in both arabidopsis and Nicotiana benthamiana plants. Also, the antiviral PTI response exhibited by AsES in arabidopsis is mediated by the BAK1/SERK3 and BKK1/SERK4 co-receptors. Moreover, AsES requires a fully active salicylic acid (SA) signalling pathway to restrict the TMV movement by inducing callose deposition. Additionally, treatment with PSP1, a biostimulant based on AsES as the active compound, showed an increased resistance against TMV in N. benthamiana and tobacco plants.

CONCLUSIONS

AsES is a fungal serine protease which triggers antiviral responses relying on a conserved mechanism by means of the SA signalling pathway and could be exploited as an effective and sustainable biotechnology strategy for viral disease management in plants.

Application of machine learning in understanding plant virus pathogenesis: trends and perspectives on emergence, diagnosis, host-virus interplay and management

Background

Inclusion of high throughput technologies in the field of biology has generated massive amounts of data in the recent years. Now, transforming these huge volumes of data into knowledge is the primary challenge in computational biology. The traditional methods of data analysis have failed to carry out the task. Hence, researchers are turning to machine learning based approaches for the analysis of high-dimensional big data. In machine learning, once a model is trained with a training dataset, it can be applied on a testing dataset which is independent. In current times, deep learning algorithms further promote the application of machine learning in several field of biology including plant virology.

Main body

Plant viruses have emerged as one of the principal global threats to food security due to their devastating impact on crops and vegetables. The emergence of new viral strains and species help viruses to evade the concurrent preventive methods. According to a survey conducted in 2014, plant viruses are anticipated to cause a global yield loss of more than thirty billion USD per year. In order to design effective, durable and broad-spectrum management protocols, it is very important to understand the mechanistic details of viral pathogenesis. The application of machine learning enables precise diagnosis of plant viral diseases at an early stage. Furthermore, the development of several machine learning-guided bioinformatics platforms has primed plant virologists to understand the host-virus interplay better. In addition, machine learning has tremendous potential in deciphering the pattern of plant virus evolution and emergence as well as in developing viable control options.

Conclusions

Considering a significant progress in the application of machine learning in understanding plant virology, this review highlights an introductory note on machine learning and comprehensively discusses the trends and prospects of machine learning in the diagnosis of viral diseases, understanding host-virus interplay and emergence of plant viruses.

Effects of the noncoding subgenomic RNA of red clover necrotic mosaic virus in virus infection

In recent years, a new class of viral noncoding subgenomic RNA (ncsgRNA) has been identified. This RNA is generated as a stable degradation product via an exoribonuclease-resistant RNA (xrRNA) structure, which blocks the progression of 5′→3′ exoribonuclease on viral RNAs in infected cells. Here, we assess the effects of the ncsgRNA of red clover necrotic mosaic virus (RCNMV), called SR1f, in infected plants. We demonstrate the following: (i) the absence of SR1f reduces symptoms and decreases viral RNA accumulation in Nicotiana benthamiana and Arabidopsis thaliana plants; (ii) SR1f has an essential function other than suppression of RNA silencing; and (iii) the cytoplasmic exoribonuclease involved in mRNA turnover, XRN4, is not required for SR1f production or virus infection. A comparative transcriptomic analysis in N. benthamiana infected with wild-type RCNMV or an SR1f-deficient mutant RCNMV revealed that wild-type RCNMV infection, which produces SR1f and much higher levels of virus, has a greater and more significant impact on cellular gene expression than the SR1f-deficient mutant. Upregulated pathways include plant hormone signaling, plant-pathogen interaction, MAPK signaling, and several metabolic pathways, while photosynthesis-related genes were downregulated. We compare this to host genes known to participate in infection by other tombusvirids. Viral reads revealed a 10- to 100-fold ratio of positive to negative strand, and the abundance of reads of both strands mapping to the 3′ region of RCNMV RNA1 support the premature transcription termination mechanism of synthesis for the coding sgRNA. These results provide a framework for future studies of the interactions and functions of noncoding RNAs of plant viruses.

IMPORTANCE Knowledge of how RNA viruses manipulate host and viral gene expression is crucial to our understanding of infection and disease. Unlike viral protein-host interactions, little is known about the control of gene expression by viral RNA. Here, we begin to address this question by investigating the noncoding subgenomic RNA (ncsgRNA) of red clover necrotic mosaic virus (RCNMV), called SR1f. Similar exoribonuclease-resistant RNAs of flaviviruses are well studied, but the roles of plant viral ncsgRNAs, and how they arise, are poorly understood. Surprisingly, we find the likely exonuclease candidate, XRN4, is not required to generate SR1f, and we assess the effects of SR1f on virus accumulation and symptom development. Finally, we compare the effects of infection by wild-type RCNMV versus an SR1f-deficient mutant on host gene expression in Nicotiana benthamiana, which reveals that ncsgRNAs such as SR1f are key players in virus-host interactions to facilitate productive infection.

A rice LRR receptor-like protein associates with its adaptor kinase OsSOBIR1 to mediate plant immunity against viral infection

Plants sense pathogen attacks using a variety of receptors at the cell surface. The LRR receptor-like proteins (RLP) and receptor-like kinases (RLK) are widely reported to participate in plant defence against bacterial and fungal pathogen invasion. However, the role of RLP and RLK in plant antiviral defence has rarely been reported. We employed a high-throughput-sequencing approach, transgenic rice plants and viral inoculation assays to investigate the role of OsRLP1 and OsSOBIR1 proteins in rice immunity against virus infection. The transcript of a rice LRR receptor-like protein, OsRLP1, was markedly up-regulated following infection by RBSDV, a devastating pathogen of rice and maize. Viral inoculation on various OsRLP1 mutants demonstrated that OsRLP1 modulates rice resistance against RBSDV infection. It was also shown that OsRLP1 is involved in the RBSDV-induced defence response by positively regulating the activation of MAPKs and PTI-related gene expression. OsRLP1 interacted with a receptor-like kinase OsSOBIR1, which was shown to regulate the PTI response and rice antiviral defence. Our results offer a novel insight into how a virus-induced receptor-like protein and its adaptor kinase activate the PTI response and antiviral defence in rice.

How activated NLRs induce anti-microbial defenses in plants

Plants utilize cell-surface localized and intracellular leucine-rich repeat (LRR) immune receptors to detect pathogens and to activate defense responses, including transcriptional reprogramming and the initiation of a form of programmed cell death of infected cells. Cell death initiation is mainly associated with the activation of nucleotide-binding LRR receptors (NLRs). NLRs recognize the presence or cellular activity of pathogen-derived virulence proteins, so-called effectors. Effector-dependent NLR activation leads to the formation of higher order oligomeric complexes, termed resistosomes. Resistosomes can either form potential calcium-permeable cation channels at cellular membranes and initiate calcium influxes resulting in activation of immunity and cell death or function as NADases whose activity is needed for the activation of downstream immune signaling components, depending on the N-terminal domain of the NLR protein. In this mini-review, the current knowledge on the mechanisms of NLR-mediated cell death and resistance pathways during plant immunity is discussed.

Geminivirus-Host Interactions: Action and Reaction in Receptor-Mediated Antiviral Immunity

In plant−virus interactions, the plant immune system and virulence strategies are under constant pressure for dominance, and the balance of these opposing selection pressures can result in disease or resistance. The naturally evolving plant antiviral immune defense consists of a multilayered perception system represented by pattern recognition receptors (PRR) and resistance (R) proteins similarly to the nonviral pathogen innate defenses. Another layer of antiviral immunity, signaling via a cell surface receptor-like kinase to inhibit host and viral mRNA translation, has been identified as a virulence target of the geminivirus nuclear shuttle protein. The Geminiviridae family comprises broad-host range viruses that cause devastating plant diseases in a large variety of relevant crops and vegetables and hence have evolved a repertoire of immune-suppressing functions. In this review, we discuss the primary layers of the receptor-mediated antiviral immune system, focusing on the mechanisms developed by geminiviruses to overcome plant immunity.

Receptor-like kinase BAM1 facilitates early movement of the Tobacco mosaic virus

Cell-to-cell movement is an important step for initiation and spreading of virus infection in plants. This process occurs through the intercellular connections, termed plasmodesmata (PD), and is usually mediated by one or more virus-encoded movement proteins (MP) which interact with multiple cellular factors, among them protein kinases that usually have negative effects on MP function and virus movement. In this study, we report physical and functional interaction between MP of Tobacco mosaic virus (TMV), the paradigm of PD-moving proteins, and a receptor-like kinase BAM1 from Arabidopsis and its homolog from Nicotiana benthamiana. The interacting proteins accumulated in the PD regions, colocalizing with a PD marker. Reversed genetics experiments, using BAM1 gain-of-function and loss-of-function plants, indicated that BAM1 is required for efficient spread and accumulation the virus during initial stages of infection of both plant species by TMV. Furthermore, BAM1 was also required for the efficient cell-to-cell movement of TMV MP, suggesting that BAM1 interacts with TMV MP to support early movement of the virus. Interestingly, this role of BAM1 in viral movement did not require its protein kinase activity. Thus, we propose that association of BAM1 with TMV MP at PD facilitates the MP transport through PD, which, in turn, enhances the spread of the viral infection.

Geminiviral Triggers and Suppressors of Plant Antiviral Immunity

Geminiviruses are circular single-stranded DNA plant viruses encapsidated into geminate virion particles, which infect many crops and vegetables and, hence, represent significant agricultural constraints worldwide. To maintain their broad-range host spectrum and establish productive infection, the geminiviruses must circumvent a potent plant antiviral immune system, which consists of a multilayered perception system represented by RNA interference sensors and effectors, pattern recognition receptors (PRR), and resistance (R) proteins. This recognition system leads to the activation of conserved defense responses that protect plants against different co-existing viral and nonviral pathogens in nature. Furthermore, a specific antiviral cell surface receptor signaling is activated at the onset of geminivirus infection to suppress global translation. This review highlighted these layers of virus perception and host defenses and the mechanisms developed by geminiviruses to overcome the plant antiviral immunity mechanisms.

Genome-Wide Association Mapping of bc-1 and bc-u Reveals Candidate Genes and New Adjustments to the Host-Pathogen Interaction for Resistance to Bean Common Mosaic Necrosis Virus in Common Bean

Bean common mosaic necrosis virus (BCMNV) is a major disease in common bean (Phaseolus vulgaris L.). Host plant resistance is the primary disease control. We sought to identify candidate genes to better understand the host-pathogen interaction and develop tools for marker-assisted selection (MAS). A genome-wide association study (GWAS) approach using 182 lines from a race Durango Diversity Panel (DDP) challenged by BCMNV isolates NL-8 [Pathogroup (PG)-III] and NL-3 (PG-VI), and genotyped with 1.26 million single-nucleotide polymorphisms (SNPs), revealed significant peak regions on chromosomes Pv03 and Pv05, which correspond to bc-1 and bc-u resistance gene loci, respectively. Three candidate genes were identified for NL-3 and NL-8 resistance. Side-by-side receptor-like protein kinases (RLKs), Phvul.003G038700 and Phvul.003G038800 were candidate genes for bc-1. These RLKs were orthologous to linked RLKs associated with virus resistance in soybean (Glycine max). A basic Leucine Zipper (bZIP) transcription factor protein is the candidate gene for bc-u. bZIP protein gene Phvul.005G124100 carries a unique non-synonymous mutation at codon 14 in the first exon (Pv05: 36,114,516 bases), resulting in a premature termination codon that causes a nonfunctional protein. SNP markers for bc-1 and bc-u and new markers for I and bc-3 genes were used to genotype the resistance genes underpinning BCMNV phenotypes in the DDP, host group (HG) differentials, and segregating F₃ families. Results revealed major adjustments to the current host-pathogen interaction model: (i) there is only one resistance allele bc-1 for the Bc-1 locus, and differential expression of the allele is based on presence vs. absence of bc-u; (ii) bc-1 exhibits dominance and incomplete dominance; (iii) bc-1 alone confers resistance to NL-8; (iv) bc-u was absent from HGs 2, 4, 5, and 7 necessitating a new gene symbol bc-u ^d to reflect this change; (v) bc-u ^d alone delays susceptible symptoms, and when combined with bc-1 enhanced resistance to NL-3; and (vi) bc-u ^d is on Pv05, not Pv03 as previously thought. These candidate genes, markers, and adjustments to the host-pathogen interaction will facilitate breeding for resistance to BCMNV and related Bean common mosaic virus (BCMV) in common bean.

Recent advances on the plant manipulation by geminiviruses

As intracellular parasites, viruses co-opt the molecular machinery of the cells they infect in order to multiply and spread, and the extensiveness and effectiveness of this manipulation ultimately determine the outcome of the interaction between virus and host. Members of the Geminiviridae family, causal agents of devastating diseases in crops, encode only a handful of multifunctional, fast-evolving proteins, which efficiently target host proteins to re-wire plant development and physiology and enable replication and spread of the viral genome. In this review, we offer an overview of the different steps in the geminiviral invasion of the host plant, and explore the knowns and unknowns in geminivirus biology.

The C4 Protein from Tomato Yellow Leaf Curl Virus Can Broadly Interact with Plant Receptor-Like Kinases

Plant receptor-like kinases (RLKs) exert an essential function in the transduction of signals from the cell exterior to the cell interior, acting as important regulators of plant development and responses to environmental conditions. A growing body of evidence suggests that RLKs may play relevant roles in plant-virus interactions, although the details and diversity of effects and underlying mechanisms remain elusive. The C4 protein from different geminiviruses has been found to interact with RLKs in the CLAVATA 1 (CLV1) clade. However, whether C4 can interact with RLKs in other subfamilies and, if so, what the biological impact of such interactions might be, is currently unknown. In this work, we explore the interaction landscape of C4 from the geminivirus Tomato yellow leaf curl virus within the Arabidopsis RLK family. Our results show that C4 can interact with RLKs from different subfamilies including, but not restricted to, members of the CLV1 clade. Functional analyses of the interaction of C4 with two well-characterized RLKs, FLAGELLIN SENSING 2 (FLS2) and BRASSINOSTEROID INSENSITIVE 1 (BRI1), indicate that C4 might affect some, but not all, RLK-derived outputs. The results presented here offer novel insight on the interface between RLK signaling and the infection by geminiviruses, and point at C4 as a potential broad manipulator of RLK-mediated signaling.

Perspectives on intracellular perception of plant viruses

The intracellular nucleotide-binding domain leucine-rich repeat (NLR) class of immune receptors plays an important role in plant viral defence. Plant NLRs recognize viruses through direct or indirect association of viral proteins, triggering a downstream defence response to prevent viral proliferation and movement within the plant. This review focuses on current knowledge of intracellular perception of viral pathogens, activation of NLRs and the downstream signalling components involved in plant viral defence.