Rice Stripe Mosaic Disease: Characteristics and Control Strategies

Rice stripe mosaic virus hijacks rice heading-related gene to promote the overwintering of its insect vector

Rice stripe mosaic virus (RSMV) is an emerging pathogen which significantly reduces rice yields in the southern region of China. It is transmitted by the leafhopper Recilia dorsalis, which overwinters in rice fields. Our field investigations revealed that RSMV infection causes delayed rice heading, resulting in a large number of green diseased plants remaining in winter rice fields. This creates a favorable environment for leafhoppers and viruses to overwinter, potentially contributing to the rapid spread and epidemic of the disease. Next, we explored the mechanism by which RSMV manipulates the developmental processes of the rice plant. A rice heading-related E3 ubiquitin ligase, Heading date Associated Factor 1 (HAF1), was found to be hijacked by the RSMV-encoded P6. The impairment of HAF1 function affects the ubiquitination and degradation of downstream proteins, HEADING DATE 1 and EARLY FLOWERING3, leading to a delay in rice heading. Our results provide new insights into the development regulation-based molecular interactions between virus and plant, and highlights the importance of understanding virus-vector-plant tripartite interactions for effective disease management strategies.

Reduced cold tolerance of viral-infected leafhoppers attenuates viral persistent epidemics

Most arthropod-borne viruses produce intermittent epidemics in infected plants. However, the underlying mechanisms of these epidemics are unclear. Here, we demonstrated that rice stripe mosaic virus (RSMV), a viral pathogen, significantly increases the mortality of its overwintering vector, the leafhopper species Recilia dorsalis. Cold-stress assays indicated that RSMV reduces the cold tolerance of leafhoppers, a process associated with the downregulation of leafhopper cuticular protein genes. An RSMV-derived small RNA (vsiR-t00355379) was found to facilitate the downregulation of a leafhopper endocuticle gene that is mainly expressed in the abdomen (named RdABD-5) and is conserved across dipteran species. The downregulation of RdABD-5 expression in R. dorsalis resulted in fewer and thinner endocuticle lamellae, leading to decreased cold tolerance. This effect was correlated with a reduced incidence rate of RSMV in early-planted rice plants. These findings contribute to our understanding of the mechanism by which viral pathogens reduce cold tolerance in arthropod vectors and suggest an approach to managing the fluctuating prevalence of arboviruses.

IMPORTANCE

Increasing arthropod vector dispersal rates have increased the susceptibility of crop to epidemic viral diseases. However, the incidence of some viral diseases fluctuates annually. In this study, we demonstrated that a rice virus reduces the cold tolerance of its leafhopper vector, Recilia dorsalis. This effect is linked to the virus-derived small RNA-mediated downregulation of a gene encoding a leafhopper abdominal endocuticle protein. Consequently, the altered structural composition of the abdominal endocuticle reduces the overwinter survival of leafhoppers, resulting in a lower incidence of RSMV infection in early-planted rice plants. Our findings illustrate the important roles of RNA interference in virus-vector insect-environment interactions and help explain the annual fluctuations of viral disease epidemics in rice fields.

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.

A critical review on bioaerosols-dispersal of crop pathogenic microorganisms and their impact on crop yield

Bioaerosols are potential sources of pathogenic microorganisms that can cause devastating outbreaks of global crop diseases. Various microorganisms, insects and viroids are known to cause severe crop diseases impeding global agro-economy. Such losses threaten global food security, as it is estimated that almost 821 million people are underfed due to global crisis in food production. It is estimated that global population would reach 10 billion by 2050. Hence, it is imperative to substantially increase global food production to about 60% more than the existing levels. To meet the increasing demand, it is essential to control crop diseases and increase yield. Better understanding of the dispersive nature of bioaerosols, seasonal variations, regional diversity and load would enable in formulating improved strategies to control disease severity, onset and spread. Further, insights on regional and global bioaerosol composition and dissemination would help in predicting and preventing endemic and epidemic outbreaks of crop diseases. Advanced knowledge of the factors influencing disease onset and progress, mechanism of pathogen attachment and penetration, dispersal of pathogens, life cycle and the mode of infection, aid the development and implementation of species-specific and region-specific preventive strategies to control crop diseases. Intriguingly, development of R gene-mediated resistant varieties has shown promising results in controlling crop diseases. Forthcoming studies on the development of an appropriately stacked R gene with a wide range of resistance to crop diseases would enable proper management and yield. The article reviews various aspects of pathogenic bioaerosols, pathogen invasion and infestation, crop diseases and yield.

Rhabdovirus encoded glycoprotein induces and harnesses host antiviral autophagy for maintaining its compatible infection

Macroautophagy/autophagy has been recognized as a central antiviral defense mechanism in plant, which involves complex interactions between viral proteins and host factors. Rhabdoviruses are single-stranded RNA viruses, and the infection causes serious harm to public health, livestock, and crop production. However, little is known about the role of autophagy in the defense against rhabdovirus infection by plant. In this work, we showed that Rice stripe mosaic cytorhabdovirus(RSMV) activated autophagy in plants and that autophagy served as an indispensable defense mechanism during RSMV infection. We identified RSMV glycoprotein as an autophagy inducer that interacted with OsSnRK1B and promoted the kinase activity of OsSnRK1B on OsATG6b. RSMV glycoprotein was toxic to rice cells and its targeted degradation by OsATG6b-mediated autophagy was essential to restrict the viral titer in plants. Importantly, SnRK1-glycoprotein and ATG6-glycoprotein interactions were well-conserved between several other rhabdoviruses and plants. Together, our data support a model that SnRK1 senses rhabdovirus glycoprotein for autophagy initiation, while ATG6 mediates targeted degradation of viral glycoprotein. This conserved mechanism ensures compatible infection by limiting the toxicity of viral glycoprotein and restricting the infection of rhabdoviruses.Abbreviations: AMPK: adenosine 5'-monophosphate (AMP)-activated protein kinase; ANOVA: analysis of variance; ATG: autophagy related; AZD: AZD8055; BiFC: bimolecular fluorescence complementation; BYSMV: barley yellow striate mosaic virus; Co-IP: co-immunoprecipitation; ConA: concanamycin A; CTD: C-terminal domain; DEX: dexamethasone; DMSO: dimethyl sulfoxide; G: glycoprotein; GFP: green fluorescent protein; MD: middle domain; MDC: monodansylcadaverine; NTD: N-terminal domain; OE: over expression; Os: Oryza sativa; PBS: phosphate-buffered saline; PtdIns3K: class III phosphatidylinositol-3-kinase; qRT-PCR: quantitative real-time reverse-transcription PCR; RFP: red fluorescent protein; RSMV: rice stripe mosaic virus; RSV: rice stripe virus; SGS3: suppressor of gene silencing 3; SnRK1: sucrose nonfermenting1-related protein kinase1; SYNV: sonchus yellow net virus; TEM: transmission electron microscopy; TM: transmembrane region; TOR: target of rapamycin; TRV: tobacco rattle virus; TYMaV: tomato yellow mottle-associated virus; VSV: vesicular stomatitis virus; WT: wild type; Y2H: yeast two-hybrid; YFP: yellow fluorescent protein.

On-site and visual detection of sorghum mosaic virus and rice stripe mosaic virus based on reverse transcription-recombinase-aided amplification and CRISPR/Cas12a

Rapid, sensitive and visual detection of plant viruses is conducive to effective prevention and control of plant viral diseases. Therefore, combined with reverse transcription and recombinase-aided amplification, we developed a CRISPR/Cas12a-based visual nucleic acid detection system targeting sorghum mosaic virus and rice stripe mosaic virus, which cause harm to crop production in field. When the RT-RAA products were recognized by crRNA and formed a complex with LbCas12a, the ssDNA labeled with a quenched green fluorescent molecule will be cleaved by LbCas12a, and then a significant green fluorescence signal will appear. The entire detection process can be completed within 30 min without using any sophisticated equipment and instruments. The detection system could detect samples at a dilution of 10⁷, about 10⁴-fold improvement over RT-PCR, so the system was successfully to detect rice stripe mosaic virus in a single leafhopper, which is the transmission vector of the virus. Finally, the CRISPR/Cas12a-based detection system was utilized to on-site detect the two viruses in the field, and the results were fully consistent with that we obtained by RT-PCR in laboratory, demonstrating that it has the application prospect of detecting important crop viruses in the field.

A Review of Vector-Borne Rice Viruses

Rice (Oryza sativa L.) is one of the major staple foods for global consumption. A major roadblock to global rice production is persistent loss of crops caused by plant diseases, including rice blast, sheath blight, bacterial blight, and particularly various vector-borne rice viral diseases. Since the late 19th century, 19 species of rice viruses have been recorded in rice-producing areas worldwide and cause varying degrees of damage on the rice production. Among them, southern rice black-streaked dwarf virus (SRBSDV) and rice black-streaked dwarf virus (RBSDV) in Asia, rice yellow mottle virus (RYMV) in Africa, and rice stripe necrosis virus (RSNV) in America currently pose serious threats to rice yields. This review systematizes the emergence and damage of rice viral diseases, the symptomatology and transmission biology of rice viruses, the arm races between viruses and rice plants as well as their insect vectors, and the strategies for the prevention and control of rice viral diseases.

Identification and Characterization of Two Novel Noda-like Viruses from Rice Plants Showing the Dwarfing Symptom

Nodaviruses are small bipartite RNA viruses and are considered animal viruses. Here, we identified two novel noda-like viruses (referred to as rice-associated noda-like virus 1 (RNLV1) and rice-associated noda-like virus 2 (RNLV2)) in field-collected rice plants showing a dwarfing phenotype through RNA-seq. RNLV1 genome consists of 3335 nt RNA1 and 1769 nt RNA2, and RNLV2 genome consists of 3279 nt RNA1 and 1525 nt RNA2. Three conserved ORFs were identified in each genome of the two novel viruses, encoding an RNA-dependent RNA polymerase, an RNA silencing suppressor, and a capsid protein, respectively. The results of sequence alignment, protein domain prediction, and evolutionary analysis indicate that these two novel viruses are clearly different from the known nodaviruses, especially the CPs. We have also determined that the B2 protein encoded by the two new noda-like viruses can suppress RNA silencing in plants. Two reverse genetic systems were constructed and used to show that RNLV1 RNA1 can replicate in plant cells and RNLV1 can replicate in insect Sf9 cells. We have also found two unusual peptidase family A21 domains in the RNLV1 CP, and RNLV1 CP can self-cleave in acidic environments. These findings provide new knowledge of novel nodaviruses.

Rice Gall Dwarf Virus Promotes the Propagation and Transmission of Rice Stripe Mosaic Virus by Co-infected Insect Vectors

Rice stripe mosaic virus (RSMV), a newly discovered plant cytorhabdovirus, and rice gall dwarf virus (RGDV), a plant reovirus, are transmitted by leafhopper Recilia dorsalis in a persistent-propagative manner. In this study, field surveys in Luoding city, Guangdong province of southern China, showed that RSMV and RGDV frequently co-infected rice plants. Furthermore, this co-infection had a synergistic effect on viral replication potential and pathogenicity in rice plants. Meanwhile, RSMV and RGDV also co-infected R. dorsalis vectors, and RGDV significantly promoted the propagation of RSMV in co-infected vectors. Accordingly, co-infection significantly promoted the acquisition and transmission efficiencies of RSMV by R. dorsalis. However, such co-infection did not significantly affect the propagation of RGDV in vectors. More importantly, we also observed that non-viruliferous R. dorsalis preferred to feed on co-infected rice plants, and this process further affected the feeding behavior of R. dorsalis to enhance viral release into rice phloem. These results provided the clues as to why RSMV had been a gradually expanding problem, creating an increasing risk of damage to rice production. Our findings revealed that synergism between RSMV and RGDV in their host and vector enhanced the propagation and transmission of RSMV, which will help guide the formulation of viral control strategies.