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 plant intracellular immune receptor mediates broad-spectrum resistance by recognizing a small conserved PAMP-like region within the pathogen protein.

Plant viruses move through plasmodesmata to infect new cells. The plant endoplasmic reticulum (ER) is interconnected among cells via the ER desmotubule in the plasmodesma across the cell wall, forming a continuous ER network throughout the entire plant. This ER continuity is unique to plants and has been postulated to serve as a platform for the intercellular trafficking of macromolecules. In the present study, the contribution of the plant ER membrane transport system to the intercellular trafficking of the NSm movement protein and Tomato spotted wilt tospovirus (TSWV) is investigated. We showed that TSWV NSm is physically associated with the ER membrane in Nicotiana benthamiana plants. An NSm-GFP fusion protein transiently expressed in single leaf cells was trafficked into neighboring cells. Mutations in NSm that impaired its association with the ER or caused its mis-localization to other subcellular sites inhibited cell-to-cell trafficking. Pharmacological disruption of the ER network severely inhibited NSm-GFP trafficking but not GFP diffusion. In the Arabidopsis thaliana mutant rhd3 with an impaired ER network, NSm-GFP trafficking was significantly reduced, whereas GFP diffusion was not affected. We also showed that the ER-to-Golgi secretion pathway and the cytoskeleton transport systems were not involved in the intercellular trafficking of TSWV NSm. Importantly, TSWV cell-to-cell spread was delayed in the ER-defective rhd3 mutant, and this reduced viral infection was not due to reduced replication. On the basis of robust biochemical, cellular and genetic analysis, we established that the ER membrane transport system serves as an important direct route for intercellular trafficking of NSm and TSWV. Plant viruses may use different host cell transport machineries to move from one cell to another through plasmodesmata. The contribution of host cell transport systems to the intercellular movement of multipartite negative-strand RNA plant viruses including tospoviruses is poorly understood. We used Tomato spotted wilt tospovirus (TSWV) as a model to understand the mechanism of intercellular movement of tospoviruses. In this study, using in vitro and in vivo systems for characterizing membrane proteins, we identified that the TSWV NSm movement protein was physically associated with the ER membrane. NSm expressed in a single leaf cell was able to move into neighboring cells along the ER membrane network. The ER membrane in plants is a unique structure that runs between neighboring cells via the ER desmotubule of the plasmodesmata and forms a continuous network throughout the plant. Taking advantage of TSWV NSm being tightly associated with ER membrane and trafficked between cells through plasmodesmata, we demonstrated here by robust biochemical, cellullar and genetic evidence that the ER membrane transport system of plants serves as an important route for intercellular trafficking of the NSm movement protein and TSWV. Our findings have important new implications for mechanistic studies on intercellular trafficking of tospoviruses and other multipartite negative-strand RNA plant viruses.

Negative-stranded/ambisense RNA viruses (NSVs) include not only dangerous pathogens of medical importance but also serious plant pathogens of agronomic importance. Tomato spotted wilt virus (TSWV) is one of the most important plant NSVs, infecting more than 1,000 plant species, and poses major threats to global food security. The segmented negative-stranded/ambisense RNA genomes of TSWV, however, have been a major obstacle to molecular genetic manipulation. In this study, we report the complete recovery of infectious TSWV entirely from complementary DNA (cDNA) clones. First, a replication- and transcription-competent minigenome replication system was established based on 35S-driven constructs of the S₍₋₎-genomic (g) or S₍₊₎-antigenomic (ag) RNA template, flanked by the 5′ hammerhead and 3′ ribozyme sequence of hepatitis delta virus, a nucleocapsid (N) protein gene and codon-optimized viral RNA-dependent RNA polymerase (RdRp) gene. Next, a movement-competent minigenome replication system was developed based on M₍₋₎-gRNA, which was able to complement cell-to-cell and systemic movement of reconstituted ribonucleoprotein complexes (RNPs) of S RNA replicon. Finally, infectious TSWV and derivatives carrying eGFP reporters were rescued in planta via simultaneous expression of full-length cDNA constructs coding for S₍₊₎-agRNA, M₍₋₎-gRNA, and L₍₊₎-agRNA in which the glycoprotein gene sequence of M₍₋₎-gRNA was optimized. Viral rescue occurred with the addition of various RNAi suppressors including P19, HcPro, and γb, but TSWV NSs interfered with the rescue of genomic RNA. This reverse genetics system for TSWV now allows detailed molecular genetic analysis of all aspects of viral infection cycle and pathogenicity. Significance Although reverse genetics (RG) systems were first developed for animal-infecting viruses with segmented negative-stranded/ambisense RNA genomes over 20 years ago, such a system for plant viruses with segmented negative-stranded/ambisense RNA genomes had not been developed until now. Tomato spotted wilt virus (TSWV), a virus with tripartite negative-stranded/ambisense RNA genomes, is one of the most economically important plant viruses in the world. Many groups have tried to construct infectious clones for TSWV, but all have failed. Here we report the establishment of a RG system for TSWV. Infectious TSWV and derivatives carrying eGFP reporters were rescued entirely from complementary DNA (cDNA) clones. This RG system now provides a powerful platform to study the disease pathology of Tospoviruses during natural infection.