Profiling Of MicroRNA Transcriptome And RT-PCR Detection Of Two Nucleolar Genes Of Rice Plants During RDV Infection

MicroRNAs (miRNAs) are genomically encoded small non-coding RNAs that regulate flow of genetic information by controlling translation or stability of mRNAs or other ill defined mechanisms. They play important roles in plant development, signal transduction and stress responses. Many studies showed that virus infection leads to the microRNA pathway malfunction in the infected plants. Alteration of the microRNA pathway has been considered one of the most important mechanisms of viral patogenesis, although currently it is not known whether such alterations are coincidental or diliberate.RDV (Rice Dwarf Virus) is one of the most important rice infecting viruses, which causes great yield losses in some areas. Symptoms associated with RDV infection include severe dwarfism, increased tilling and white chlorotic specks on the infected leaves. These phynotypes strikingly resemble those resulted from microRNA pathway mutants. In this study, transcriptome of the microRNAs of RDV infectd rice plants were profiled, using mock inoculated rice plants as control. The results showed that RDV infection had marginal effects on rice micro RNA metabolism. Only one mieroRNA, miR397, showed morderate upregulation in RDV infected rice plants, implying that microRNAs might be not important in RDV pathogenesis.Recent transcriptome analysises of virus infected plants revealed that increased expression of a set of ribosomal genes might be a general response of plants to many viruses. Considering the fact that many viruses encode nucleolus-targeting products and the well established role of nucleolus in ribosomal biogenesis. Posibility of the alteration of nucleolar physiology in virus infected plants were investigated by detecting changes of two nucleolar genes using RT-PCR. These two genes were a gene encoding fibrillarin, one of the three most abundant proteins in the nucleolus and a gene encoding nucleolar Nop5, a component common to the box C/D small nucleolar ribonucleoproteins. The results showed that both of the two genes were significantly upregulated in RDV infected rice plants. This suggested that nucleolus might be a target of RDV infection. Implications of the nucleolus-targeting of RDV infection were disscussed.