The Mechanisms Of Cell-To-Cell Movement Of Tomato Spotted Wilt Virus And Inhibition Of Virus Movement By Immune Receptor Sw-5b

Tomato spotted wilt virus(TS WV),as a tripartite negative stranded RNA virus,which is considered to be one of the most devastating plant viruses,and causes 1 billion dollars of crop economic losses every year and is distributed in Yunnan and other areas in China.TSWV encodes movement protein to help the virus to move and infect,and there have been few reports of host factors required for viral movement.The disease-resistant protein Sw-5b of tomato has immunity to TSWV,however whether Sw-5b has a direct inhibitory effect on the movement of TSWV and the corresponding inhibition mechanism remains poorly understood.In order to explore these molecular biological problems,this study mainly focuses on the following two aspects:1.Molecular Co-Chaperone SGT1 is critical for cell-to-cell movement and systemic infection of tomato spotted wilt virus in Nicotiana benthamiana.Successful virus infection in plant requires many host factors.To date,very few host factors have been identified as important in Tospovirus infection in plants.We reported earlier that NSm protein plays critical roles in viral cell-to-cell and long-distance movement.In this study,we determined that molecular co-chaperone NbSGT1 interacted with TSWV NSm in Nicotiana benthamiana.TSWV infection significantly upregulated the expression of NbSGT1 gene and transient overexpression of NbSGT1 in N.benthamiana leaves accelerated TSWV infection.In contrast,silencing the NbSGT1 gene expression using a virus-induced gene silencing(VIGS)approach strongly inhibited TSWV NSm cell-to-cell movement,as well as TSWV local and systemic infection in N.benthamiana plants.Furthermore,NbSGT1 was found to regulate the infection of both American and Euro/Asia type tospoviruses in N.benthamiana plant.Collectively,our findings presented in this paper and the results published previously indicated that molecular co-chaperone NbSGT1 plays important roles in modulating both positive stranded and tripartite negative stranded RNA virus infection in plants.2.The mechanism of tomato disease resistant protein Sw-5b inhibit cell-to-cell movement of virus.In order to analyze the disease resistance mechanism of tomato resistance protein Sw-5b to Tomato spotted wilt virus,this study determined whether Sw-5b inhibited TSWV movement protein NSm.We found that Sw-5b can directly inhibit cell-to-cell movement of NSm,and the number of NSm localized to plasmodesmata was significantly reduced in the presence of Sw-5b.In order to elucidate its underlying molecular mechanism,the transcriptome analysis revealed that when Sw-5b was activated,and the genes involved in plant cell wall expansion were down-regulated,and the down-regulation of these genes directly inhibited the cell-to-cell movement of the virus.To further understand the molecular regulation mechanism,we found that the promoter region of these cell wall genes contains WRKY transcription factor binding sites by analyzing cell wall-related genes.The transcriptome data indicated that Sw-5b activated the WRKYs gene after activation by NSm.The electrophoretic mobility shift assay revealed that the WRKYs transcription factor bind to the promoter of the cell wall-associated gene.Overexpression of WRKYs inhibits the expression of cell wall-associated genes,indicating that WRKYs transcription factors negatively regulate cell wall genes.At the same time,this study also found that Sw-5b-induced upregulation of WRKYs transcription factors is dependent on the jasmonic acid pathway,but not on the salicylic acid pathway.Through VIGS,it was found that Sw-5b lost its ability to resist TSWV infection after silencing WRKYs transcription factor,indicating that WRKYs transcription factor plays an important regulatory role in Sw-5b-mediated disease resistance.In conclusion,this study revealed the molecular mechanism by which WRKYs regulate down-regulation of cell wall-associated genes and mediates resistance to TSWV after activation of Sw-5b resistance protein.