Transcriptional alterations in model host, Nicotiana benthamiana, in response to infection by South African cassava mosaic virus

Successful systemic infection by plant viruses is the outcome of complex molecular interactions between host and viral pathogen, leading to spatial and temporal alterations in plant gene expression. Results from a microarray study using the commercially available custom-made 60-mer oligo NimbleGen Platform (representing 13 014 ESTs) (Roche) revealed that expression levels of many transcripts were altered in response to SACMV at 21 dpi (representing full systemic infection), including encoded proteins involved in transcription networks, defence responses and plant hormone signalling. Approximately 4.7 % (611 of 13 014) of the transcripts were significantly altered in response to SACMV infection. Of these, 483 genes were found to be induced and 128 genes were suppressed. GOslim functional group analysis illustrated that differentially expressed genes in infected leaf tissue, compared to mock inoculated, were primarily overrepresented in the cellular component category for nuclear (19.92 %) and other cellular components (14 %), while categories corresponding to transferase activity (14.42 %) and other binding (13.43 %) were overrepresented for Molecular Function. Cellular processes (24.93 %) and other metabolic processes (18.05 %) were overrepresented for Biological Process. Notably from our data, we were able to detect transcript changes in several defence-related and sucrose/starch metabolic pathways. Collectively, alterations in genes associated with the cytoskeleton, cell wall and plasmodesmata, namely myosin heavy chain, beta-tubulin, Ras-GTPase (Rab6A), ß-1,3-glucanase, pectinesterase and pectate lyase, suggest possible roles in intracellular vesicle-assisted movement to the plasmamembrane and release into the adjacent cell via the plasmodesmata (Pd).