Rice Ragged Stunt Virus Propagation and Infection on Rice Plants

Plasmodesmata-associated Flotillin positively regulates broad-spectrum virus cell-to-cell trafficking

Viral diseases seriously threaten rice production. Plasmodesmata (PD)-associated proteins are deemed to play a key role in viral infection in host plants. However, few PD-associated proteins have been discovered in rice to afford viral infection. Here, inspired by the infection mechanism in insect vectors, we identified a member of the Flotillin family taking part in the cell-to-cell transport of rice stripe virus (RSV) in rice. Flotillin1 interacted with RSV nucleocapsid protein (NP) and was localized on PD. In flotillin1 knockout mutant rice, which displayed normal growth, RSV intercellular movement was retarded, leading to significantly decreased disease incidence. The PD pore sizes of the mutant rice were smaller than those of the wild type due to more callose deposits, which was closely related to the upregulation of two callose synthase genes. RSV infection stimulated flotillin1 expression and enlarged the PD aperture via RSV NP. In addition, flotillin1 knockout decreased disease incidences of southern rice black-streaked dwarf virus (SRBSDV) and rice dwarf virus (RDV) in rice. Overall, our study reveals a new PD-associated protein facilitating virus cell-to-cell trafficking and presents the potential of flotillin1 as a target to produce broad-spectrum antiviral rice resources in the future.

Review: Plant microRNAs in pathogen defense: A panacea or a piece of the puzzle?

Plant microRNAs (miRNAs) control key agronomic traits that are associated with their conserved role(s) in development. However, despite a multitude of studies, the utility of miRNAs in plant-pathogen resistance remains less certain. Reviewing the literature identifies three general classes of miRNAs regarding plant pathogen defense. Firstly, a number of evolutionary dynamic 22 nucleotide miRNA families that repress large numbers of plant immunity genes, either directly, or through triggering the biogenesis of secondary siRNAs. However, understanding of their role in defense and of their manipulation to enhance pathogen resistance are still lacking. Secondly, highly conserved miRNAs that indirectly impact disease resistance through their targets that are primarily regulating development or hormone signaling. Any alteration of these miRNAs usually results in pleiotropic impacts, which may alter disease resistance in some plant species, and against some pathogens. Thirdly, are the comparatively diverse and evolutionary dynamic set of non-conserved miRNAs, some of which contribute to pathogen resistance, but whose narrow evolutionary presence will likely restrict their utility. Therefore, reflecting the diverse and evolving nature of plant-pathogen interactions, a complex interplay of plant miRNAs with pathogen responses exists. Any miRNA-based solution for pathogen resistance will likely be highly specific, rather than a general panacea.

The immune response mechanism of Nilaparvata lugens against a combined infection of rice ragged stunt virus and Metarhizium anisopliae

BACKGROUND

Previous studies of brown planthopper (BPH), Nilaparvata lugens, showed that carrying the plant pathogenic virus, rice ragged stunt virus (RRSV), enhanced the lethality of the entomopathogenic fungus, Metarhizium anisopliae (YTTR). The underlying mechanism for this was not established but a serine protease cascade was hypothesized to be involved.

RESULTS

Two immune response genes, NlKPI and NlVenomase, were identified and shown to be involved. The synthesized double-strand RNA (dsRNA) techniques used in this study to explore gene function revealed that treatment with dsRNA to silence either gene led to a higher BPH mortality from M. anisopliae infection than the dsRNA control treatment. NlKPI and NlVenomase play vital roles in BPH immunity to defend against alien pathogens. Both genes participate in the immune response process of BPH against co-infection with RRSV and M. anisopliae YTTR by regulating the expression of antimicrobial peptides and phenoloxidase activity.

CONCLUSION

Our study provided new targets for BPH biocontrol and laid a solid foundation for further research on the interaction of virus-insect-EPF (entomopathogenic fungus). © 2023 Society of Chemical Industry.

Immune Responses and Transcriptomic Analysis of Nilaparvata lugens against Metarhizium anisopliae YTTR Mediated by Rice Ragged Stunt Virus

Plant viruses and entomopathogenic fungi (EPF) can both elicit immune responses in insects. This study was designed to clarify whether plant viruses could affect the efficacy of EPF and explore the immune responses of brown planthopper (BPH), Nilaparvata lugens, in response to different pathogen infections. In this study, a strain of Metarhizium anisopliae YTTR with high pathogenicity against BPH was selected and explored whether rice ragged stunt virus (RRSV) could affect its lethality against BPH. RNA-seq was used to detect the inner responses of BPH in response to RRSV and M. anisopliae YTTR infection. Results showed that M. anisopliae YTTR has strong lethality against BPH (RRSV-carrying and RRSV-free). RRSV invasion did not affect the susceptibility of BPH against M. anisopliae YTTR at all concentrations. At 1 × 108 spores/mL, M. anisopliae YTTR caused a cumulative mortality of 80% to BPH at 7 days post-treatment. The largest numbers of differentially expressed genes (DEGs) was obtained in BPH treated with the two pathogens than in other single pathogen treatment. In addition, KEGG enrichment analysis showed that the DEGs were mostly enriched in immune and physiological mechanisms-related pathways. Both RRSV and M. anisopliae YTTR could induce the expression changes of immune-related genes. However, most of the immune genes had varying expression patterns in different treatment. Our findings demonstrated that RRSV invasion did not have any significant effect on the pathogenicity of M. anisopliae YTTR, while the co-infection of M. anisopliae YTTR and RRSV induced more immune and physiological mechanisms -related genes' responses. In addition, the presence of RRSV could render the interplay between BPH and M. anisopliae YTTR more intricate. These findings laid a basis for further elucidating the immune response mechanisms of RRSV-mediated BPH to M. anisopliae infection.