Virus-Induced Symptoms in Plants: A Review of Interactions Between Viral Trafficking and RNA Silencing
Viruses in plants have to accomplish two movement stages: cell-to-cell transfer from infected cells to neighboring healthy cells and long-distance transport from source to sink via the vascular system to establish systemic infection. Plants also activate defense mechanisms to combat viral invasion. Recent advances in three main aspects of virus interaction with the host plant are focal in this review: first, the viral distribution in host plants including the essential components required for viral movement; second, indications that the molecular defense mechanism known as RNA silencing plays an important role in controlling those viral distributions and is counteracted by virus-encoded suppressor proteins; and third, accumulated current knowledge on how viral resistance by RNA silencing relates to developing disease-free tissues during the infection period. Although one potential control of viral diseases in crops is to use virus-tolerant cultivars, a knowledge of viral distributions and the interactions between RNA silencing and virus-encoded counter-defenses is valuable.
Key Words: plant defense, RNA silencing, silencing suppressor, siRNA, viral distribution, viral movement
Abbreviations: CMV – Cucumber mosaic virus, DCL – Dicer-Like Protein, DGI – dark green islands, dsRNA – double- stranded RNA, HC-Pro – helper component proteinase, MPs – movement proteins, PD – plasmodesmata, PTGS – post- transcriptional gene silencing, RDR – RNA-dependent RNA polymerase, RISC – RNA-induced silencing complex, RNA – ribonucleic acid, SEL – size exclusion limit, siRNA – small interfering RNA, ssRNA – single-stranded RNA, TMV – Tobacco mosaic virus, TSWV – Tomato spotted wilt virus, TYLCV – Tomato yellow leaf curl virus, vRNP – viral ribonucleoprotein, YTs – yellow green tissues