Alteration of host-encoded miRNAs in virus infected plants—experimentally verified

This chapter highlights the host-encoded miRNAs and their mRNA targets in response to viral infection in a susceptible plant. A common set of miRNAs, mainly those related to plant development or described as responsive to different biotic and abiotic stresses, was summarized. miR168 was up-regulated by virus infection in a plant- and virus-independent manner. However, many miRNAs and their targets respond to viral infection in a virus-, strain-, plant- and tissue-specific manner. Novel miRNAs were even identified in virus-infected plants. Certain miRNAs may serve as potential biomarkers for virus infection. To date, miRNAs were not identified in plant viruses. Virus infection may cause plant Argonaute quenching and global changes in Dicer homeostasis. In virus-infected plants, the levels of miRNAs and their mRNA targets were altered antagonistically. However, in some cases, a parallel increase in the levels of target mRNAs, and the corresponding miRNA species, was observed. Moreover, some miRNAs and their targets exhibited a biphasic expression pattern. At an early stage of infection, when no virus was detected systemically, certain miRNAs were down-regulated along with up-regulation of the mRNA targets. The later stage of infection included higher levels of both miRNAs and their targets, as well as virus accumulation. In addition, interference of viral silencing suppressors with the miRNA pathway seems to be a general feature in virus–plant interaction, although functioning by distinct mechanisms.