Differential RNA-silencing and plasmodesmata callose deposition in leaves and stems of transgenic tobacco plants duringTobacco etch virusinfection recovery

Abstract

ABSTRACTViruses are amongst the most prevalent pathogens that threaten plants. Plants have evolved a sequence-specific defence mechanism against viruses to ensure survival, known as RNA silencing, which includes transcriptional and post-transcriptional gene silencing. After a viral infection, plants can undergo the process of recovery, and become further resistant to viral infection after a new systemic infection. This study aimed to identify additional mechanisms underlying disease recovery besides the known RNA silencing. Thus, we analyzed the transgenic tobacco plants for thetobacco etch virus(TEV) expressing a transcript derived from the Nuclear Inclusion “a” protein (NIa) cistron of TEV, which had recovered from infection three weeks following viral inoculation. Performingin situhybridizations, we detected the virus and the transgene-derived transcript in stem sections adjacent to the recovered leaves. To further understand the silenced and non-silenced conditions in leaf and stem, we undertook tissue-specific RNA-Seq and small RNA-Seq analyses in these tissues, and found a higher number of differentially expressed genes (DEGs) in the recovered leaf related to defence, silencing, and hormone signaling responses. Finally, we observed differences in plasmodesmata callose deposition and callose-related genes. Overall, the findings of the present study suggest that cell-to-cell viral restriction movement also participates in the recovery of TEV infection in transgenic tobacco plants, besides the key function of RNA silencing.IMPORTANCEHost recovery from a viral infection is a common strategy to ensure survival. In plants and other eukaryotes, this phenomenon has been strongly related to RNA silencing. However, the role of other defense mechanisms remains unexplored. Recovery has been studied in leaves where is visually observed. The implications of other organs such as the stem remain poorly understood. We give insights into differential RNA silencing occurring between leaves and stems. This study demonstrated that additional mechanisms, such as overexpression of defense-related genes and callose accumulation in plasmodesmata, during recovery are involved, besides RNA silencing.