Abstract
MicroRNAs (miRNAs) are non-coding RNAs of approximately 20–24 nucleotides in length that serve as central regulators of eukaryotic gene expression by targeting mRNAs for cleavage or translational repression. In plants, miRNAs are associated with numerous regulatory pathways in growth and development processes, and defensive responses in plant–pathogen interactions. Recently, significant progress has been made in understanding miRNA-mediated gene silencing and how viruses counter this defense mechanism. Here, we summarize the current knowledge and recent advances in understanding the roles of miRNAs involved in the plant defense against viruses and viral counter-defense. We also document the application of miRNAs in plant antiviral defense. This review discusses the current understanding of the mechanisms of miRNA-mediated gene silencing and provides insights on the never-ending arms race between plants and viruses.
Highlights
Viruses are among the most important causal agents of infectious diseases in both animals and plants
Synthesis of phased, secondary small interfering RNAs (siRNAs) from the N coding sequence through overexpression of miR6019 was shown to be accompanied by reductions in N transcript accumulation and N-mediated resistance against TMV (Li et al, 2012). These results suggest that the miRNA-mediated gene silencing response is integrated with R gene–mediated antiviral defense responses
Most viral suppressors of RNA silencing (VSRs)-mediated inhibition of RNA silencing occurs through two modes of action: (1) some VSRs sequester small RNA duplexes by binding to short or long dsRNAs, resulting in the suppression of the assembly of AGOs into RNA-induced silencing complex (RISC); (2) some VSRs physically interact with Argonaute 1 (AGO1) to prevent siRNA or miRNA loading, impede slicing activity, or degrade the AGO1 protein (Burgyan and Havelda, 2011; Wang et al, 2012; Moon and Park, 2016)
Summary
Viruses are among the most important causal agents of infectious diseases in both animals and plants. Most VSR-mediated inhibition of RNA silencing occurs through two modes of action: (1) some VSRs sequester small RNA duplexes by binding to short or long dsRNAs, resulting in the suppression of the assembly of AGOs into RISCs; (2) some VSRs physically interact with AGO1 to prevent siRNA or miRNA loading, impede slicing activity, or degrade the AGO1 protein (Burgyan and Havelda, 2011; Wang et al, 2012; Moon and Park, 2016). A study demonstrated that Rice stripe virus (RSV) infections influenced small RNA profiles in rice, and that RSV induced the expression of novel miRNAs from conserved miRNA precursors (Du et al, 2011) These results suggest that VSRs and viral infection lead to major changes in the miRNA-mediated gene silencing pathway in plants. Invading viruses can trigger the production of plant endogenous miRNAs. In addition to repressing the expression of host genes, the miRNAs can target viral mRNA for degradation. Far, engineering of amiRNA for antiviral resistance has been used successfully in various plant species, including N. benthamiana (Qu et al, 2007; Ai et al, 2011; Kung et al, 2012; Ali et al, 2013; Song et al, 2014; Mitter et al, 2016; Wagaba et al, 2016; Carbonell and Daros, 2017), Arabidopsis (Duan et al, 2008; Lin et al, 2009), rice (Sun et al, 2016), wheat
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