Abstract
Post-transcriptional gene regulation by small RNAs is now established as an important branch of the gene regulatory system. Many different classes of small RNAs have been discovered; among these are short interfering RNAs (siRNAs) and microRNA (miRNAs). Though differences in the processing and function of small RNAs exist between plants and animals, both groups utilize small RNA-mediated gene regulation in response to pathogens. Host encoded miRNAs and siRNAs are generated from viral RNA function in host defense and pathogenic resistance in plants. In animals, miRNAs are key regulators in both immune system development and in immune function. Pathogens, in particular viruses, have evolved mechanisms to usurp the host’s small RNA-mediated regulatory system. Overall, small RNAs are a major component of host defense and immunity in eukaryotes. The goal of this review is to summarize our current knowledge of the involvement of eukaryotic small RNA pathways in host defense and viral pathogenesis.
Highlights
Post-transcriptional gene regulation by small RNAs is established as an important branch of the gene regulatory system
The major endogenous class of small RNAs involved in regulating the immune response and immune system development in animals consists of miRNAs
Bacterial infections can alter miRNA expression, including miR-393, miR-167, miR-160 and miR-825 [13]. These miRNAs regulate the expression of auxin signaling genes, as well as biotic stress-related genes, which are associated with PAMP signaling
Summary
There are several classes of small RNA families, and of these, short-interfering RNAs (siRNAs) and microRNAs (miRNAs) are the major small RNA groups associated with eukaryotic immunity. For siRNAs, the precursor molecule for Dicer processing is a longer dsRNA, while the miRNA precursor is an RNA hairpin [1]. (RDR6) produces dsRNAs from miRNA-mediated cleavage products of TAS gene transcripts These dsRNAs are processed into trans-acting siRNAs (tasiRNAs) by DCL4. Viral RNAs are utilized by RDR6 to produce dsRNAs, which are processed into siRNAs by DCL2 These viral siRNAs undergo a second round of RDR6 amplification and are transported to peripheral sites, where they form RISCs with either AGO1 or AGO2. These RISCs degrade viral RNA as part of the anti-viral response; (B) MicroRNA biogenesis pathway of animal cells.
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