Abstract
RNA silencing, an evolutionarily conserved and sequence-specific gene-inactivation system, has a pivotal role in antiviral defense in most eukaryotic organisms. In plants, a class of exogenous small RNAs (sRNAs) originating from the infecting virus called virus-derived small interfering RNAs (vsiRNAs) are predominantly responsible for RNA silencing-mediated antiviral immunity. Nowadays, the process of vsiRNA formation and the role of vsiRNAs in plant viral defense have been revealed through deep sequencing of sRNAs and diverse genetic analysis. The biogenesis of vsiRNAs is analogous to that of endogenous sRNAs, which require diverse essential components including dicer-like (DCL), argonaute (AGO), and RNA-dependent RNA polymerase (RDR) proteins. vsiRNAs trigger antiviral defense through post-transcriptional gene silencing (PTGS) or transcriptional gene silencing (TGS) of viral RNA, and they hijack the host RNA silencing system to target complementary host transcripts. Additionally, several applications that take advantage of the current knowledge of vsiRNAs research are being used, such as breeding antiviral plants through genetic engineering technology, reconstructing of viral genomes, and surveying viral ecology and populations. Here, we will provide an overview of vsiRNA pathways, with a primary focus on the advances in vsiRNA biogenesis and function, and discuss their potential applications as well as the future challenges in vsiRNAs research.
Highlights
In plants and other eukaryotic organisms, small RNAs have emerged as key players of RNA silencing in the regulation of various biological processes, including plant growth and development, host immunity and pathogen virulence
HUA ENHANCER1 (HEN1), zinc finger protein SERRATE (SE), dsRNA-binding protein HYPONASTIC LEAVES 1 (HYL1), G-patch domain-containing protein TOUGH (TGH), HEN1 SUPPRESSOR1 (HESO1) and a family of SMALL-RNA DEGRADING NUCLEASES (SDNs) reviewed in Xie et al (2015). small interfering RNAs (siRNAs) are divided into four subgroups: trans-acting siRNAs, heterochromatic-associated siRNAs, natural antisense transcript siRNAs, and virusactivated siRNAs, which are primarily generated from diverse perfectly double-stranded RNA precursors and excised by DICERLIKE 1 (DCL1) and its homologs (DCL2, DCL3, and DCL4) either cooperatively or redundantly (Bouche et al, 2006; Axtell, 2013; Cao et al, 2014). small RNAs (sRNAs) are recruited by an ARGONAUTE (AGO) ribonucleoprotein complex, referred to as the RNAinduced silencing complex (RISC; Poulsen et al, 2013; Carbonell and Carrington, 2015)
It indicates that the biogenesis of virus-derived small interfering RNAs (vsiRNAs) is analogous to that of endogenous sRNAs, which requires the actions of various DCLs, RNA-dependent RNA polymerase (RDR), and AGOs
Summary
In plants and other eukaryotic organisms, small RNAs (sRNAs) have emerged as key players of RNA silencing in the regulation of various biological processes, including plant growth and development, host immunity and pathogen virulence. What is known has been deduced based on the insights from genetic analysis in Arabidopsis and vsiRNAs profiling from various plant species. It indicates that the biogenesis of vsiRNAs is analogous to that of endogenous sRNAs, which requires the actions of various DCLs, RDRs, and AGOs. Table 1 lists the specific plant DCLs, RDRs, and AGOs known to contribute to the biogenesis of vsiRNAs
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