Rice black streaked dwarf virus P7-2 forms a SCF complex through binding to Oryza sativa SKP1-like proteins, and interacts with GID2 involved in the gibberellin pathway

Gibberellin Positively Regulates Tomato Resistance to Tomato Yellow Leaf Curl Virus (TYLCV)

Tomato yellow leaf curl virus (TYLCV) is a prominent viral pathogen that adversely affects tomato plants. Effective strategies for mitigating the impact of TYLCV include isolating tomato plants from the whitefly, which is the vector of the virus, and utilizing transgenic lines that are resistant to the virus. In our preliminary investigations, we observed that the use of growth retardants increased the rate of TYLCV infection and intensified the damage to the tomato plants, suggesting a potential involvement of gibberellic acid (GA) in the conferring of resistance to TYLCV. In this study, we employed an infectious clone of TYLCV to inoculate tomato plants, which resulted in leaf curling and growth inhibition. Remarkably, this inoculation also led to the accumulation of GA3 and several other phytohormones. Subsequent treatment with GA3 effectively alleviated the TYLCV-induced leaf curling and growth inhibition, reduced TYLCV abundance in the leaves, enhanced the activity of antioxidant enzymes, and lowered the reactive oxygen species (ROS) levels in the leaves. Conversely, the treatment with PP333 exacerbated TYLCV-induced leaf curling and growth suppression, increased TYLCV abundance, decreased antioxidant enzyme activity, and elevated ROS levels in the leaves. The analysis of the gene expression profiles revealed that GA3 up-regulated the genes associated with disease resistance, such as WRKYs, NACs, MYBs, Cyt P450s, and ERFs, while it down-regulated the DELLA protein, a key agent in GA signaling. In contrast, PP333 induced gene expression changes that were the opposite of those caused by the GA3 treatment. These findings suggest that GA plays an essential role in the tomato's defense response against TYLCV and acts as a positive regulator of ROS scavenging and the expression of resistance-related genes.

Plant virology in the 21st century in China: Recent advances and future directions

Plant viruses are a group of intracellular pathogens that persistently threaten global food security. Significant advances in plant virology have been achieved by Chinese scientists over the last 20 years, including basic research and technologies for preventing and controlling plant viral diseases. Here, we review these milestones and advances, including the identification of new crop-infecting viruses, dissection of pathogenic mechanisms of multiple viruses, examination of multilayered interactions among viruses, their host plants, and virus-transmitting arthropod vectors, and in-depth interrogation of plant-encoded resistance and susceptibility determinants. Notably, various plant virus-based vectors have also been successfully developed for gene function studies and target gene expression in plants. We also recommend future plant virology studies in China.

Ubiquitin-Dependent and Independent Proteasomal Degradation in Host-Pathogen Interactions

Ubiquitin, a small protein, is well known for tagging target proteins through a cascade of enzymatic reactions that lead to protein degradation. The ubiquitin tag, apart from its signaling role, is paramount in destabilizing the modified protein. Here, we explore the complex role of ubiquitin-mediated protein destabilization in the intricate proteolysis process by the 26S proteasome. In addition, the significance of the so-called ubiquitin-independent pathway and the role of the 20S proteasome are considered. Next, we discuss the ubiquitin-proteasome system's interplay with pathogenic microorganisms and how the microorganisms manipulate this system to establish infection by a range of elaborate pathways to evade or counteract host responses. Finally, we focus on the mechanisms that rely either on (i) hijacking the host and on delivering pathogenic E3 ligases and deubiquitinases that promote the degradation of host proteins, or (ii) counteracting host responses through the stabilization of pathogenic effector proteins.

The Plant Ubiquitin-Proteasome System as a Target for Microbial Manipulation

The plant immune system perceives pathogens to trigger defense responses. In turn, pathogens secrete effector molecules to subvert these defense responses. The initiation and maintenance of defense responses involve not only de novo synthesis of regulatory proteins and enzymes but also their regulated degradation. The latter is achieved through protein degradation pathways such as the ubiquitin-proteasome system (UPS). The UPS regulates all stages of immunity, from the perception of the pathogen to the execution of the response, and, therefore, constitutes an ideal candidate for microbial manipulation of the host. Pathogen effector molecules interfere with the plant UPS through several mechanisms. This includes hijacking general UPS functions or perturbing its ability to degrade specific targets. In this review, we describe how the UPS regulates different immunity-related processes and how pathogens subvert this to promote disease.

Molecular insights into the responses of barley to yellow mosaic disease through transcriptome analysis

BACKGROUND

Barley (Hordeum vulgare L.) represents the fourth most essential cereal crop in the world, vulnerable to barley yellow mosaic virus (BaYMV) and/or barley mild mosaic virus (BaMMV), leading to the significant yield reduction. To gain a better understanding of the mechanisms regarding barley crop tolerance to virus infection, we employed a transcriptome sequencing approach and investigated global gene expression among three barley varieties under both infected and control conditions.

RESULTS

High-throughput sequencing outputs revealed massive genetic responses, reflected by the barley transcriptome after BaYMV and/or BaMMV infection. Significant enrichments in peptidase complex and protein processing in endoplasmic reticulum were clustered through Gene ontology and KEGG analysis. Many genes were identified as transcription factors, antioxidants, disease resistance genes and plant hormones and differentially expressed between infected and uninfected barley varieties. Importantly, general response genes, variety-specific and infection-specific genes were also discovered. Our results provide useful information for future barley breeding to resist BaYMV and BaMMV.

CONCLUSIONS

Our study elucidates transcriptomic adaptations in barley response to BaYMV/BaMMV infection through high-throughput sequencing technique. The analysis outcome from GO and KEGG pathways suggests that BaYMV disease induced regulations in multiple molecular-biology processes and signalling pathways. Moreover, critical DEGs involved in defence and stress tolerance mechanisms were displayed. Further functional investigations focusing on these DEGs contributes to understanding the molecular mechanisms of plant response to BaYMV disease infection, thereby offering precious genetic resources for breeding barley varieties resistant to BaYMV disease.

Transcriptional and post-transcriptional regulation of RNAi-related gene expression during plant-virus interactions

As sessile organisms, plants encounter diverse invasions from pathogens including viruses. To survive and thrive, plants have evolved multilayered defense mechanisms to combat virus infection. RNAi, also known as RNA silencing, is an across-kingdom innate immunity and gene regulatory machinery. Molecular framework and crucial roles of RNAi in antiviral defense have been well-characterized. However, it is largely unknown that how RNAi is transcriptionally regulated to initiate, maintain and enhance cellular silencing under normal or stress conditions. Recently, insights into the transcriptional and post-transcriptional regulation of RNAi-related genes in different physiological processes have been emerging. In this review, we integrate these new findings to provide updated views on how plants modulate RNAi machinery at the (post-) transcriptional level to respond to virus infection.

The gibberellic acid derived from the plastidial MEP pathway is involved in the accumulation of Bamboo mosaic virus

A gene upregulated in Nicotiana benthamiana after Bamboo mosaic virus (BaMV) infection was revealed as 1-deoxy-d-xylulose-5-phosphate reductoisomerase (NbDXR). DXR is the key enzyme in the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway that catalyzes the conversion of 1-deoxy-d-xylulose 5-phosphate to 2-C-methyl-d-erythritol-4-phosphate. Knockdown and overexpression of NbDXR followed by BaMV inoculation revealed that NbDXR is involved in BaMV accumulation. Treating leaves with fosmidomycin, an inhibitor of DXR function, reduced BaMV accumulation. Subcellular localization confirmed that DXR is a chloroplast-localized protein by confocal microscopy. Furthermore, knockdown of 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase, one of the enzymes in the MEP pathway, also reduced BaMV accumulation. The accumulation of BaMV increased significantly in protoplasts treated with isopentenyl pyrophosphate. Thus, the metabolites of the MEP pathway could be involved in BaMV infection. To identify the critical components involved in BaMV accumulation, we knocked down the crucial enzyme of isoprenoid synthesis, NbGGPPS11 or NbGGPPS2. Only NbGGPPS2 was involved in BaMV infection. The geranylgeranyl pyrophosphate (GGPP) synthesized by NbGGPPS2 is known for gibberellin synthesis. We confirmed this result by supplying gibberellic acid exogenously on leaves, which increased BaMV accumulation. The de novo synthesis of gibberellic acid could assist BaMV accumulation.

Fine-mapping and candidate gene analysis of a major locus controlling leaf thickness in rice (Oryza sativa L.)

Leaf thickness is an important trait in rice (Oryza sativa L.). It affects both photosynthesis and sink-resource efficiency. However, compared to leaf length and length width, reports seldom focused on leaf thickness due to the complicated measurement and minor difference. To identify the quantitative trait loci (QTL) and explore the genetic mechanism regulating the natural variation of leaf thickness, we crossed a high leaf thickness variety Aixiuzhan (AXZ) to a thin leaf thickness variety Yangdao No.6 (YD 6) and evaluated 585 F₂ individuals. We further use bulked sergeant analysis with whole-genome resequencing (BSA-seq) to identify five genomic regions, including chromosomes 1, 6, 9, 10, and 12. These regions represented significant allele frequency differentiation between thick and thin leaf thickness among the mixed pool offspring. Moreover, we conducted a linkage mapping using 276 individuals derived from the F₂ population. We fine-mapped and confirmed that chromosome 9 contributed the primary explanation of phenotypic variance. We fine-mapped the candidate regions and confirmed that the chromosome 9 region contributed to flag leaf thickness in rice. We observed the virtual cellular slices and found that the bundle sheath cells in YD 6 flag leaf veins are fewer than AXZ. We analyzed the potential regions on chromosome 9 and narrowed the QTL candidate intervals in the 928-kb region. Candidate genes of this major QTL were listed as potentially controlled leaf thickness. These results provide promising evidence that cloning leaf thickness is associated with yield production in rice.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11032-022-01275-y.

Rescue of an Infectious cDNA Clone of Barley Yellow Dwarf Virus-GAV

Barley yellow dwarf virus-GAV (BYDV-GAV) is one of the most prevalent viruses causing yellow dwarf disease in wheat in China. The biology and pathology of BYDV-GAV are well studied; however, gene functions and molecular mechanisms of BYDV-GAV disease development are unclear because of the lack of a reverse genetics system. In this study, a full-length complementary DNA (cDNA) clone of BYDV-GAV was constructed and expressed via Agrobacterium-mediated inoculation of Nicotiana benthamiana. Virions produced by BYDV-GAV in N. benthamiana were transmitted to wheat by an aphid vector after acquisition via a sandwich feeding method. Infectivity of the cDNA clone in wheat was verified via reverse transcription PCR and western blot assays, and the recombinant virus elicited typical reddening symptoms in oats and was transmitted between wheat plants. These results confirm the production of biologically active transmissible virions. Using the BYDV-GAV infectious clone, we demonstrate that viral protein P4 was involved in cell-to-cell movement and stunting symptoms in wheat. This is the first report describing the development of an infectious full-length cDNA clone of BYDV-GAV and provides a useful tool for virus-host-vector interaction studies.

Tomato chlorosis virus-encoded p22 suppresses auxin signalling to promote infection via interference with SKP1-Cullin-F-boxTIR1 complex assembly

Phytohormone auxin plays a fundamental role in plant growth and defense against pathogens. However, how auxin signalling is regulated during virus infection in plants remains largely unknown. Auxin/indole-3-acetic acid (Aux/IAA) is the repressor of auxin signalling and can be recognized by an F-box protein transport inhibitor response 1 (TIR1). Ubiquitination and degradation of Aux/IAA by SKP1-Cullin-F-boxTIR1 (SCFTIR1 ) complex can trigger auxin signalling. Here, with an emerging important plant virus worldwide, we showed that tomato chlorosis virus (ToCV) infection or stable transgenic overexpression of its p22 protein does not alter auxin accumulation level but significantly decreases the expression of auxin signalling-responsive genes, suggesting that p22 can attenuate host auxin signalling. Further, p22 could bind the C-terminal of SKP1.1 and compete with TIR1 to interfere with the SCFTIR1 complex assembly, leading to a suppression of Aux/IAA degradation. Silencing and over-expression assays suggested that both NbSKP1.1 and NbTIR1 suppress ToCV accumulation and disease symptoms. Altogether, ToCV p22 disrupts the auxin signalling through destabilizing SCFTIR1 by interacting with the C-terminal of NbSKP1.1 to promote ToCV infection. Our findings uncovered a previously unknown molecular mechanism employed by a plant virus to manipulate SCF complex-mediated ubiquitin pathway and to reprogram auxin signalling for efficient infection.

Virus-induced phytohormone dynamics and their effects on plant-insect interactions

Attacks on plants by both viruses and their vectors is common in nature. Yet the dynamics of the plant-virus-vector tripartite system, in particular the effects of viral infection on plant-insect interactions, have only begun to emerge in the last decade. Viruses can modulate the interactions between insect vectors and plants via the jasmonate, salicylic acid and ethylene phytohormone pathways, resulting in changes in fitness and viral transmission capacity of their insect vectors. Virus infection of plants may also modulate other phytohormones, such as auxin, gibberellins, cytokinins, brassinosteroids and abscisic acid, with yet undefined consequences on plant-insect interactions. Moreover, virus infection in plants may incur changes to other plant traits, such as nutrition and secondary metabolites, that potentially contribute to virus-associated, phytohormone-mediated manipulation of plant-insect interactions. In this article, we review the research progress, discuss issues related to the complexity and variability of the viral modulation of plant interactions with insect vectors, and suggest future directions of research in this field.

Plant Defense Networks against Insect-Borne Pathogens

Upon infection with insect-borne microbial pathogens, plants are exposed to two types of damage simultaneously. Over the past decade, numerous molecular studies have been conducted to understand how plants respond to pathogens or herbivores. However, investigations of host responses typically focus on a single stress and are performed under static laboratory conditions. In this review, we highlight research that sheds light on how plants deploy broad-spectrum mechanisms against both vector-borne pathogens and insect vectors. Among the host genes involved in multistress resistance, many are involved in innate immunity and phytohormone signaling (especially jasmonate and salicylic acid). The potential for genome editing or chemical modulators to fine-tune crop defensive signaling, to develop sustainable methods to control insect-borne diseases, is discussed.

Current understanding of the interplays between host hormones and plant viral infections

Phytohormones mediate plant development and responses to stresses caused by biotic agents or abiotic factors. The functions of phytohormones in responses to viral infection have been intensively studied, and the emerging picture of complex mechanisms provides insights into the roles that phytohormones play in defense regulation as a whole. These hormone signaling pathways are not simple linear or isolated cascades, but exhibit crosstalk with each other. Here, we summarized the current understanding of recent advances for the classical defense hormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) and also the roles of abscisic acid (ABA), auxin, gibberellic acid (GA), cytokinins (CKs), and brassinosteroids (BRs) in modulating plant–virus interactions.

Arms race between rice and viruses: a review of viral and host factors

Much is known about the molecular interactions between positive-strand RNA viruses and dicotyledon plants. However, many important viral pathogens of the monocotyledon rice crop contain negative-strand or double-strand RNA genomes. Recent studies have shown that virus-derived small-interfering RNAs (siRNAs), host microRNAs and phytohormones regulate antiviral responses in rice plants and that rice-infecting RNA viruses encode a diverse repertoire of multifunctional proteins with counter-defensive activities. Moreover, the interactions between viral virulence proteins and host susceptibility factors also shape the virus-rice arms race. This review will focus on these recent advances and discuss strategies and challenges in the translation of discoveries made on molecular virus-rice interactions into practical virus control measures.

Comparative study on cytogenetics and transcriptome between diploid and autotetraploid rice hybrids harboring double neutral genes

Double pollen fertility neutral genes, San and Sbn, can control pollen sterility in intersubspecific (indica × japonica) rice hybrids, which has excellent potential to increase rice yield. Previous studies showed that polyploidy could increase the interaction of three pollen sterility loci, i.e. Sa, Sb and Sc, which cause pollen sterility in autotetraploid rice hybrids, and hybrid fertility could be improved by double neutral genes, San and Sbn, in autotetraploid rice hybrids. We compared cytological and transcriptome data between autotetraploid and diploid rice hybrid during meiosis and single microspore stages to understand the molecular mechanism of neutral genes for overcoming pollen sterility in autotetraploid rice hybrids, which harbored double neutral genes. Cytological results revealed that the double neutral genes resulted in higher pollen fertility (76.74%) and lower chromosomal abnormalities in autotetraploid hybrid than in parents during metaphase I, metaphase II, anaphase I and anaphase II. Moreover, autotetraploid rice hybrid displayed stronger heterosis than a diploid hybrid. Compared with diploid rice hybrid, a total of 904 and 68 differently expressed genes (DEGs) were identified explicitly in autotetraploid hybrid at meiosis and single microspore stages, respectively. Of these, 133 and 41 genes were detected in higher-parent dominance and transgressive up-regulation dominance, respectively, which were considered autotetraploid potential heterosis genes, including a meiosis-related gene (Os01g0917500, MSP1) and two meiosis specific-genes (Os07g0624900 and Os04g0208600). Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genomes pathway (KEGG) analysis revealed that DEGs significantly enriched in amino acid metabolism and photosynthesis metabolism. These results indicated that meiosis-specific and meiosis-related genes, and amino acids and photosynthesis metabolism-related genes contribute to higher yield and pollen fertility in autotetraploid rice hybrid. This study provides a theoretical basis for molecular mechanisms of heterosis in autotetraploid rice harboring double neutral genes for pollen fertility.

Begomovirus-Associated Betasatellite Virulence Factor βC1 Attenuates Tobacco Defense to Whiteflies via Interacting With Plant SKP1

Plant-mediated interactions between plant viruses and their vectors are important determinants of the population dynamics of both types of organisms in the field. The whitefly Bemisia tabaci can establish mutualism with begomoviruses via their shared host plants. This mutualism is achieved by the interaction between virulence factors and their host proteins. While the virulence factor βC1 encoded by tomato yellow leaf curl China betasatellite (TYLCCNB), a subviral agent associated to the begomovirus tomato yellow leaf curl China virus (TYLCCNV), may interact with plant protein MYC2, thereby establishing the indirect mutualism between TYLCCNV and whitefly, whether other mechanisms are involved remains unknown. Here, we found the in vitro and in vivo interactions between βC1 and tobacco protein S-phase kinase associated protein 1 (NtSKP1). Silencing the expression of NtSKP1 enhanced the survival rate and fecundity of whiteflies on tobacco plants. NtSKP1 could activate the transcription of genes in jasmonic acid (JA) pathways by impairing the stabilization of JAZ1 protein. Moreover, βC1-NtSKP1 interaction could interfere JAZ1 degradation and attenuate the plant JA defense responses. These results revealed a novel mechanism underlying the better performance of whiteflies on TYLCCNV/TYLCCNB-infected plants.

Hijacking of host cellular components as proviral factors by plant-infecting viruses

Plant viruses are important pathogens that cause serious crop losses worldwide. They are obligate intracellular parasites that commandeer a wide array of proteins, as well as metabolic resources, from infected host cells. In the past two decades, our knowledge of plant-virus interactions at the molecular level has exploded, which provides insights into how plant-infecting viruses co-opt host cellular machineries to accomplish their infection. Here, we review recent advances in our understanding of how plant viruses divert cellular components from their original roles to proviral functions. One emerging theme is that plant viruses have versatile strategies that integrate a host factor that is normally engaged in plant defense against invading pathogens into a viral protein complex that facilitates viral infection. We also highlight viral manipulation of cellular key regulatory systems for successful virus infection: posttranslational protein modifications for fine control of viral and cellular protein dynamics; glycolysis and fermentation pathways to usurp host resources, and ion homeostasis to create a cellular environment that is beneficial for viral genome replication. A deeper understanding of viral-infection strategies will pave the way for the development of novel antiviral strategies.

Rice black-streaked dwarf virus-encoded P5-1 regulates the ubiquitination activity of SCF E3 ligases and inhibits jasmonate signaling to benefit its infection in rice

SCF (Skp1/Cullin1/F-box) complexes are key regulators of many cellular processes. Viruses encode specific factors to interfere with or hijack these complexes and ensure their infection in plants. The molecular mechanisms controlling this interference/hijack are currently largely unknown. Here, we present evidence of a novel strategy used by Rice black-streaked dwarf virus (RBSDV) to regulate ubiquitination in rice (Oryza sativa) by interfering in the activity of OsCSN5A. We also show that RBSDV P5-1 specifically affects CSN-mediated deRUBylation of OsCUL1, compromising the integrity of the SCF^COI1 complex. We demonstrate that the expressions of jasmonate (JA) biosynthesis-associated genes are not inhibited, whereas the expressions of JA-responsive genes are down-regulated in transgenic P5-1 plants. More importantly, application of JA to P5-1 transgenic plants did not reduce their susceptibility to RBSDV infection. Our results suggest that P5-1 inhibits the ubiquitination activity of SCF E3 ligases through an interaction with OsCSN5A, and hinders the RUBylation/deRUBylation of CUL1, leading to an inhibition of the JA response pathway and an enhancement of RBSDV infection in rice.

Cucurbit Chlorotic Yellows Virus p22 Protein Interacts with Cucumber SKP1LB1 and Its F-Box-Like Motif Is Crucial for Silencing Suppressor Activity

Plants use RNA silencing as a defense against viruses. In response, viruses encode various RNA silencing suppressors to counteract the antiviral silencing. Here, we identified p22 as a silencing suppressor of cucurbit chlorotic yellows crinivirus and showed that p22 interacts with CsSKP1LB1, a Cucumis sativus ortholog of S-phase kinase-associated protein 1 (SKP1). The F-box-like motif of p22 was identified through sequence analysis and found to be necessary for the interaction using a yeast two-hybrid assay. The involvement of the F-box-like motif in p22 silencing suppressor activity was determined. Proteomics analysis of Nicotiana benthamiana leaves expressing p22, and its F-box-like motif deletion mutant showed 228 differentially expressed proteins and five enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways: ABC transporters, sesquiterpenoid and triterpenoid biosynthesis, ubiquitin-mediated proteolysis, riboflavin metabolism, and cysteine and methionine metabolism. Collectively, our results demonstrate the interaction between p22 and CsSKP1LB1 and show that the deletion of F-box-like motif inhibits p22 silencing suppressor activity. The possible pathways regulated by the p22 through the F-box-like motif were identified using proteomics analysis.

The Dual Effect of the Brassinosteroid Pathway on Rice Black-Streaked Dwarf Virus Infection by Modulating the Peroxidase-Mediated Oxidative Burst and Plant Defense

The phytohormone brassinosteroid (BR) not only plays key roles in regulating plant growth and development but is also involved in modulating the plant defense system in response to pathogens. We previously found that BR application made rice plants more susceptible to the devastating pathogen rice black-streaked dwarf virus (RBSDV), but the mechanism of BR-mediated susceptibility remains unclear. We now show that both BR-deficient and -insensitive mutants are resistant to RBSDV infection. High-throughput sequencing showed that the defense hormone salicylic acid and jasmonic acid pathways were activated in the RBSDV-infected BR mutant. Meanwhile, a number of class III peroxidases (OsPrx) were significantly changed and basal reactive oxygen species (ROS) accumulated in BR mutants. Treatment with exogenous hormones and other chemicals demonstrated that the BR pathway could suppress the levels of OsPrx and the ROS burst by directly binding the promoters of OsPrx genes. Together, our findings indicate that BR-mediated susceptibility is at least partly caused by inhibition of the action of defense hormones, preventing the accumulation of the peroxidase-mediated oxidative burst.

Geminivirus-Associated Betasatellites: Exploiting Chinks in the Antiviral Arsenal of Plants

Betasatellites are a diverse group of circular single-stranded DNA satellites frequently associated with begomoviruses belonging to the family Geminiviridae. Challenged with a geminivirus-betasatellite infection, plants have employed sophisticated defense mechanisms to protect themselves. Betasatellites, in turn, employ mechanisms to antagonize these plant antiviral pathways. In this review, we focus on the anti-geminiviral immune pathways present both in plants and whiteflies. We also outline the counter-defensive strategies deployed by betasatellites to overcome the host defenses and initiate a successful infection. Finally, we discuss the outcomes of the opposing forces of plant immunity and betasatellite-mediated antagonism in the context of an evolutionary arms race. Understanding of the molecular dialog between plants and betasatellites will likely allow for the development of novel antiviral strategies.

Rice black-streaked dwarf virus P10 acts as either a synergistic or antagonistic determinant during superinfection with related or unrelated virus

Rice black-streaked dwarf virus (RBSDV), a member of the genus Fijivirus, is a devastating pathogen of crop plants. RBSDV S10 encodes a capsid protein (P10) that is an important component of the double-layered particle. However, little information is available on the roles of RBSDV P10 in viral infection or in interactions with other viruses. Here, we demonstrate that the expression of P10 in plants alleviates the symptoms of both RBSDV and the closely related Southern rice black-streaked dwarf virus (SRBSDV), and reduces the disease incidence, but renders the plants more susceptible to the unrelated Rice stripe virus (RSV). Further experiments suggest that P10-mediated resistance to RBSDV and SRBSDV operates at the protein level, rather than the RNA level, and is not a result of post-transcriptional gene silencing. Transcriptomic data reveal that the expression of P10 in plants significantly suppresses the expression of rice defence-related genes, which may play important roles in resistance to RSV infection. After infection with RBSDV, plants are more resistant to subsequent challenge by SRBSDV, but more susceptible to RSV. Overall, these results indicate that P10 acts as an important effector in virus interactions.

Mal de Río Cuarto virus infection causes hormone imbalance and sugar accumulation in wheat leaves

BACKGROUND

Mal de Río Cuarto virus (MRCV) infects several monocotyledonous species including maize and wheat. Infected plants show shortened internodes, partial sterility, increased tillering and reduced root length. To better understand the molecular basis of the plant-virus interactions leading to these symptoms, we combined RNA sequencing with metabolite and hormone measurements.

RESULTS

More than 3000 differentially accumulated transcripts (DATs) were detected in MRCV-infected wheat plants at 21 days post inoculation compared to mock-inoculated plants. Infected plants exhibited decreased levels of TaSWEET13 transcripts, which are involved in sucrose phloem loading. Soluble sugars, starch, trehalose 6-phosphate (Tre6P), and organic and amino acids were all higher in MRCV-infected plants. In addition, several transcripts related to plant hormone metabolism, transport and signalling were increased upon MRCV infection. Transcripts coding for GA20ox, D14, MAX2 and SMAX1-like proteins involved in gibberellin biosynthesis and strigolactone signalling, were reduced. Transcripts involved in jasmonic acid, ethylene and brassinosteroid biosynthesis, perception and signalling and in auxin transport were also altered. Hormone measurements showed that jasmonic acid, brassinosteroids, abscisic acid and indole-3-acetic acid were significantly higher in infected leaves.

CONCLUSIONS

Our results indicate that MRCV causes a profound hormonal imbalance that, together with alterations in sugar partitioning, could account for the symptoms observed in MRCV-infected plants.

Abscisic acid negatively modulates plant defence against rice black-streaked dwarf virus infection by suppressing the jasmonate pathway and regulating reactive oxygen species levels in rice

Abscisic acid (ABA) plays a multifaceted role in plant immunity and can either increase resistance or increase susceptibility to some bacterial and fungal pathogens depending on the pathosystem. ABA is also known to mediate plant defence to some viruses. In this study, the relationship between the ABA pathway and rice black-streaked dwarf virus (RBSDV) was investigated in rice. The expression of ABA pathway genes was significantly reduced upon RBSDV infection. Application of exogenous hormones and various ABA pathway mutants revealed that the ABA pathway plays a negative role in rice defence against RBSDV. Exogenous hormone treatment and virus inoculation showed that ABA inhibits the jasmonate-mediated resistance to RBSDV. ABA treatment also suppressed accumulation of reactive oxygen species by inducing the expression of superoxidase dismutases and catalases. Thus, ABA modulates the rice-RBSDV interaction by suppressing the jasmonate pathway and regulating reactive oxygen species levels. This is the first example of ABA increasing susceptibility to a plant virus.

Comparative proteomic analysis of maize (Zea mays L.) seedlings under rice black-streaked dwarf virus infection

BACKGROUND

Maize rough dwarf disease (MRDD) is a severe disease that has been occurring frequently in southern China and many other Asian countries. MRDD is caused by the infection of Rice black streaked dwarf virus (RBSDV) and leads to significant economic losses in maize production. To well understand the destructive effects of RBSDV infection on maize growth, comparative proteomic analyses of maize seedlings under RBSDV infection was performed using an integrated approach involving LC-MS/MS and Tandem Mass Tag (TMT) labeling.

RESULTS

In total, 7615 maize proteins, 6319 of which were quantified. A total of 116 differentially accumulated proteins (DAPs) were identified, including 35 up- and 81 down-regulated proteins under the RBSDV infection. Enrichment analysis showed that the DAPs were most strongly associated with cyanoamino acid metabolism, protein processing in ER, and ribosome-related pathways. Two sulfur metabolism-related proteins were significantly reduced, indicating that sulfur may participate in the resistance against RBSDV infection. Furthermore, 15 DAPs involved in six metabolic pathways were identified in maize under the RBSDV infection.

CONCLUSIONS

Our data revealed that the responses of maize to RBSDV infection were controlled by various metabolic pathways.

The Yeast Three-Hybrid System for Protein Interactions

Proteins rarely act alone as their functions tend to be regulated in vivo. Therefore, protein-protein interaction analyses provide key clues for understanding the complex biological processes in the living cell. Several techniques have been developed to elucidate the conformation of large protein complexes, dynamic protein complex rearrangement and transient protein interactions. Yeast two-hybrid system is a well-established method to analyze binary protein interactions. Here we describe a basic yeast three-hybrid method, which represents an additional refinement of the classical yeast two-hybrid system for analyzing further complex interactions among three proteins.