Submitted to: Molecular Biosystems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/3/2012
Publication Date: 6/1/2012
Citation: Moeller, J.R., Moscou, M.J., Bancroft, T., Skadsen, R.W., Wise, R.P., Whitham, S.A. 2012. Differential regulation of host mRNA translation during obligate pathogen-plant interactions. Molecular Biosystems. 8:2153-2165. Interpretive Summary: When plants are infected by a viral pathogen, certain genes are turned on or become more active, while others are turned off or made less active. Reading a gene involves making messenger RNA (mRNA) copies of the gene, which are then translated into protein and enzyme molecules by a ribosomal complex. This is the essence of gene expression, since mRNAs do nothing by themselves; it is the proteins they encode that move a cell’s biochemistry in a particular direction. Much of the knowledge of various diseases come from microarray analysis of infected tissues. This technique uses microscopic dots of synthesized DNA, representing over 20,000 genes arrayed on, essentially, a microscope slide. The microarray is used to interrogate a tissue’s mRNA population, giving a quantitative listing of which genes are turned on, and by how much. It can also reveal which genes become completely or partially turned off. In the past, the quantity of a gene’s mRNA has been taken to reflect which and how much protein is produced. However, it is only the mRNAs that are bound to ribosomes (polysomes) that are used to produce protein. The simple plant Arabidopsis thaliana provides a model system in which to study changes in gene expression resulting from viral infection; its genome is completely sequenced, and its genetics is well characterized. Turnip mosaic virus (TuMV) altered the mRNA levels from a set of genes in polysomal RNA, independently of the abundance of these mRNAs in total RNA. Approximately one-half of these mRNAs had enhanced association with polysomal RNA in response to TuMV infection, while the other half had reduced association with polysomal RNA. The picture provided by the polysomal mRNA population is likely to be a more accurate representation of the plant’s biochemical response to infection. The sequence and structure at the front end of the mRNAs may provide clues as to how plants select which mRNAs will be used for protein and enzyme production. This is the first comprehensive comparison of total versus polysomal mRNA populations during infection by an important plant virus. These results will benefit other scientists and plant breeders in formulating programs to produce disease-resistant crops.
Technical Abstract: Virus infection reprograms the plant messenger RNA (mRNA) transcriptome by activating or interfering with a variety of signaling pathways, but the effects on host mRNA translation have not been explored on a genome-wide scale. To address this issue, Arabidopsis thaliana mRNA transcripts were quantified by microarray hybridization in total RNA and polyribosomal (polysomal) RNA isolated from systemically-infected leaves at 10 days after inoculation with Turnip mosaic virus (TuMV). The mRNA transcript abundance in polysomal RNA versus total RNA provided a ratio (polysomal/total ratio) that was used to determine if association of mRNA transcripts was altered in response to TuMV infection. mRNAs for which the polysomal/total ratio was significantly altered between TuMV-infected and mock-inoculated plants were determined to be regulated at the level of translation in response to TuMV. The polysomal/total ratio of 470 transcripts was altered at the 20% false discovery rate threshold demonstrating that TuMV affects the translation of A. thaliana mRNAs. Of these transcripts, the association of 258 was enhanced with polyribosomes and 170 were suppressed. Analysis of the sequence features of these transcripts suggests that TuMV infection suppresses translation of mRNAs containing upstream AUG start codon (AUG) sequences and enhances translation of mRNAs with short 5' and 3' Untranslated Regions (UTRs).