title: Expression of geminiviral AC2 RNA silencing suppressor changes sugar and jasmonate responsive gene expression in transgenic tobacco plants.
abstract: BACKGROUND
  RNA-silencing is a conserved gene regulation and surveillance machinery, which in plants, is also used as major defence mechanism against viruses. Various virus-specific dsRNA structures are recognized by the silencing machinery leading to degradation of the viral RNAs or, as in case of begomoviruses, to methylation of their DNA genomes. Viruses produce specific RNA silencing suppressor (RSS) proteins to prevent these host defence mechanisms, and as these interfere with the silencing machinery they also disturb the endogenous silencing reactions. In this paper, we describe how expression of AC2 RSS, derived from African cassava mosaic geminivirus changes transcription profile in tobacco (Nicotiana tabacum) leaves and in flowers.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biochemistry and Food Chemistry, Laboratory of Molecular Plant Biology, University of Turku, Vesilinnantie 5, LTII, 2,floor, Turku, 20014, Finland. artsoi@utu.fi
authors.forename: Arto J
authors.initials: AJ
authors.lastname: Soitamo
authors.forename: Balaji
authors.initials: B
authors.lastname: Jada
authors.forename: Kirsi
authors.initials: K
authors.lastname: Lehto
mesh_terms: D050260:Carbohydrate Metabolism / Q000187:drug effects / Q000235:genetics*; D002734:Chlorophyll / Q000096:biosynthesis; D003517:Cyclopentanes / Q000494:pharmacology*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D035264:Flowers / Q000187:drug effects / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D016153:Genes, Suppressor; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics; D054883:Oxylipins / Q000494:pharmacology*; D010641:Phenotype; D010788:Photosynthesis / Q000187:drug effects / Q000235:genetics; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics* / Q000276:immunology / Q000821:virology*; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: C099182:AC2 protein, geminivirus; D003517:Cyclopentanes; D004268:DNA-Binding Proteins; D054883:Oxylipins; D010940:Plant Proteins; D012333:RNA, Messenger; D012269:Ribosomal Proteins; D014764:Viral Proteins; D002734:Chlorophyll; C011006:jasmonic acid; D003546:Cysteine Endopeptidases; C072775:HC-Pro protein, potyvirus