14-3-3 proteins play vital roles in plant defense against various pathogen invasions. To date, how 14-3-3 affects virus infections in plants remains largely unclear. In this study, we found that Nicotiana benthamiana 14-3-3h interacts with TRANSLATIONALLY CONTROLLED TUMOR PROTEIN (TCTP), a susceptibility factor of potato virus Y (PVY). Silencing of Nb14-3-3h facilitates PVY accumulation, whereas overexpression of Nb14-3-3h inhibits PVY replication. The antiviral activities of 3 Nb14-3-3h dimerization defective mutants are significantly decreased, indicating that dimerization of Nb14-3-3h is indispensable for restricting PVY infection. Our results also showed that the mutant Nb14-3-3h^E16A, which is capable of dimerizing but not interacting with NbTCTP, has reduced anti-PVY activity; the mutant NbTCTP^I65A, which is unable to interact with Nb14-3-3h, facilitates PVY replication compared with the wild-type NbTCTP, indicating that dimeric Nb14-3-3h restricts PVY infection by interacting with NbTCTP and preventing its proviral function. As a counter-defense, PVY 6K1 interferes with the interaction between Nb14-3-3h and NbTCTP by competitively binding to Nb14-3-3h and rescues NbTCTP to promote PVY infection. Our results provide insights into the arms race between plants and potyviruses.

Tomato mottle mosaic virus (ToMMV) poses a threat to production and quality of tomato fruits. The Tm-2² gene confers resistance to some tobamoviruses by recognizing viral movement proteins. However, Tm-2²-mediated resistance against ToMMV is not well known. Here, we found that ToMMV could infect wild-type but not Tm-2² transgenic Nicotiana benthamiana plants and could also infect tomato cultivar Moneymaker but not resistant cultivar Jili with homozygous Tm-2². Chimeric viral ToMMV^ToBRFV−MP with swapped ToMMV MP to MP of tomato brown rugose fruit virus could systemically infect Tm-2² transgenic N. benthamiana and tomato cultivars Jili plants. Further, transient expression of ToMMV MP in the leaves of Tm-2² transgenic N. benthamiana plants induced hypersensitive response-associated cell death, suggesting that the MP of ToMMV was the avirulent factor for the Tm-2² resistance gene. ToMMV could infect Tm-2²-containing cultivar Jinpeng 1 but not Chaobei. Sequence analysis revealed that cultivars Chaobei and Jinpeng 1 were heterozygous, where Chaobei consists of Tm-2² and Tm-2 genes, while Jinpeng 1 consists of Tm-2² and tm-2 genes. Transient co-expression assays showed that both Tm-2² and Tm-2 but not tm-2 could recognize ToMMV MP and induce hypersensitivity response-associated cell death in N. benthamiana leaves, suggesting that homozygous tomato harboring Tm-2² and heterozygous tomato containing Tm-2² and Tm-2 may exhibit more durable resistance to ToMMV than heterozygous tomato carrying Tm-2² and tm-2. Further, Tm-2² transgenic N. benthamiana and tomato cultivar Jili plants with silenced Tm-2² gene were susceptible to ToMMV. Also, silencing type-I J-domain MIP1 gene compromised Tm-2²-mediated resistance to ToMMV in Tm-2² transgenic N. benthamiana and tomato cultivar Jili. Moreover, we found that viral RNA could accumulate in the systemic leaves of Tm-2² transgenic N. benthamiana plants and tomato cultivar Jili at 35°C, but not at 20, 25, or 30°C. Altogether, our findings reveal that the Tm-2² confers resistance to ToMMV by recognizing MP, and the resistance is regulated by the allele combinations, accumulation levels of Tm-2², MIP1, and the temperature.

Sugarcane mosaic virus (SCMV) is the prevalent virus inducing maize dwarf mosaic and sugarcane mosaic diseases in China. According to the phylogenetic results of the complete genomic and coat protein gene sequences, SCMV was divided into four or five molecular groups, respectively. Previously, we detected SCMV isolates of group SO from Canna spp. in Ji’nan, Shandong province, China. In this study, we collected two SCMV isolates infecting Canna spp. in Ji’nan (Canna-Ji’nan) and Tai’an (Canna-Tai’an) of Shandong, China. Their complete genome sequences had genome of 9576 nucleotides and contained a large open reading frame encoding a polyprotein of 3063 amino acids. The phylogenetic analysis showed that the both Canna-Ji’nan and Canna-Tai’an were clustered into an independent group based on the complete genome sequence. In this study, we report the complete genome sequences of SCMV infecting Canna spp. from Ji’nan and Tai’an. This is the first report on SCMV belonging to SO group.

Potyviruses move to neighboring cells in the form of virus particles or a coat protein (CP)-containing ribonucleoprotein complex. However, the precise roles of RNA-binding residues in potyviral CP in viral cell-to-cell movement remain to be elucidated. In this study, we predicted the three-dimensional model of tobacco vein banding mosaic virus (TVBMV)-encoded CP and found nine residues presumably located in the CP RNA-binding pocket. Substitutions of the two basic residues at positions 192 and 225 (R¹⁹² and K²²⁵) with either alanine, cysteine, or glutamic acid abolished TVBMV cell-to-cell and systemic movement in Nicotiana benthamiana plants. These substitutions also reduced the replication of the mutant viruses. Results from the electrophoretic mobility shift assay showed that the RNA-binding activity of mutant CPs derived from R¹⁹² or K²²⁵ substitutions was significantly lower than that of wild-type CP. Analysis of purified virus particles showed that mutant viruses with R¹⁹² or K²²⁵ substitutions formed RNA-free virus-like particles. Mutations of R¹⁹² and K²²⁵ did not change the CP plasmodesmata localization. The wild-type TVBMV CP could rescue the deficient cell-to-cell movement of mutant viruses. Moreover, deletion of any of the other seven residues also abolished TVBMV cell-to-cell movement and reduced the CP RNA-binding activity. The corresponding nine residues in watermelon mosaic virus CP were also found to play essential roles in virus cell-to-cell movement. In conclusion, residues R¹⁹² and K²²⁵ in the CP RNA-binding pocket are critical for viral RNA binding and affect both virus replication and cell-to-cell movement. [ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Summary: To establish systemic infection, plant viruses must replicate, and conduct intra‐ and intercellular movement and long‐distance movement, all of which require the participation of host factors. Tobamoviruses move in the form of movement protein (MP)–viral RNA complex and utilize endocytosis for intracellular movement. However, how tobamoviral MPs hijack host factors to reach the plasma membrane (PM) and then plasmodesmata (PD) is still largely unknown. Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus that mainly infects tomatoes and peppers. Here, we show that tomato RabE1a, a small Rab GTPase, interacts with ToBRFV MP and participates in the movement of ToBRFV. Knocking out RabE1a in tomatoes could inhibit infection by ToBRFV. RabE1a positively regulates MP transport to the PM, and this transport process is regulated by its nucleotide‐binding state. Furthermore, RabE1a interacts with the exocyst subunit SEC10b to jointly regulate MP transport to the PM and intracellular movement of ToBRFV. The adaptor protein AP2β interacts with MP and transports MP from the PM to the PD for intercellular movement of ToBRFV. We further find that knocking out RabE1a could also inhibit the infection of other tobamoviruses. In summary, MP exocytosis is coregulated by RabE1a and the exocyst subunit SEC10b for transport to the PM, where it then uses AP2β‐regulated endocytosis to PD. These results provide a comprehensive overview of tobamoviral MP intracellular transport and are insightful for breeding tomato plants resistant to ToBRFV and related tobamoviruses.