Expression of geminiviral AC2 RNA silencing suppressor changes sugar and jasmonate responsive gene expression in transgenic tobacco plants

Expression of AC2 RSS in transgenic tobacco plants induced clear phenotypic changes both in leaves and in flowers. Transcriptomes of these plants were strongly altered, with total of 1118 and 251 differentially expressed genes in leaves and flowers, respectively. The three most up-regulated transcript groups were related to stress, cell wall modifications and signalling, whereas the three most down-regulated groups were related to translation, photosynthesis and transcription. It appears that many of the gene expression alterations appeared to be related to enhanced biosynthesis of jasmonate and ethylene, and consequent enhancement of the genes and pathways that are regulated by these hormones, or to the retrograde signalling caused by the reduced photosynthetic activity and sugar metabolism. Comparison of these results to a previous transcriptional profiling of HC-Pro RSS-expressing plants revealed that some of same genes were induced by both RSSs, but their expression levels were typically higher in AC2 than in HC-Pro RSS expressing plants. All in all, a large number of transcript alterations were found to be specific to each of the RSS expressing transgenic plants.AC2 RSS in transgenic tobacco plants interferes with the silencing machinery. It causes stress and defence reactions for instance via induction of the jasmonate and ethylene biosynthesis, and by consequent gene expression alteration regulated by these hormones. The changed sugar metabolism may cause significant down-regulation of genes encoding ribosomal proteins, thus reducing the general translation level.The conserved molecular machinery of RNA-silencing constitutes a very complex genetic regulatory network in all eukaryotes. The common features for these regulatory pathways are their induction by double stranded (ds) RNA sequences. In plants, these are cleaved by the RNAse III type DICER-LIKE (DCL) enzymes, assisted by HYPONASTI LEAVES1 (HYL1), SERRATE (SE) and DAWLE (DLL) proteins [1] into 21–25 nu