Abstract
Small RNAs are significant regulators of gene expression, which play multiple roles in plant development, growth, reproductive and stress response. It is generally believed that the regulation of plants’ endogenous genes by small RNAs has evolved from a cellular defense mechanism for RNA viruses and transposons. Most small RNAs have well-established roles in the defense response, such as viral response. During viral infection, plant endogenous small RNAs can direct virus resistance by regulating the gene expression in the host defense pathway, while the small RNAs derived from viruses are the core of the conserved and effective RNAi resistance mechanism. As a counter strategy, viruses evolve suppressors of the RNAi pathway to disrupt host plant silencing against viruses. Currently, several studies have been published elucidating the mechanisms by which small RNAs regulate viral defense in different crops. This paper reviews the distinct pathways of small RNAs biogenesis and the molecular mechanisms of small RNAs mediating antiviral immunity in plants, as well as summarizes the coping strategies used by viruses to override this immune response. Finally, we discuss the current development state of the new applications in virus defense based on small RNA silencing.
Highlights
During the long process of co-evolution between plants and viruses, the plant viruses, as obligate parasites with limited genome coding function, need to widely use the host intracellular metabolic system for its replication, expression, and infection establishment, as well as to obtain nutrition for proliferation at the expense of the host [1]
The complete RNA interference (RNAi) pathway can be divided into three parts: the biogenesis of sRNAs, target transcripts cleavage of RNA-induced silencing complex (RISC) complex guided by the sequence specificity of sRNAs and the transitivity of RNAi
To overcome the host defense mediated by RNAi, viruses encode viral suppressors of RNAi (VSRs) that interfere with the plant antiviral RNAi pathway (Table 1)
Summary
During the long process of co-evolution between plants and viruses, the plant viruses, as obligate parasites with limited genome coding function, need to widely use the host intracellular metabolic system for its replication, expression, and infection establishment, as well as to obtain nutrition for proliferation at the expense of the host [1]. Plants activate effector-triggered immunity (ETI) through resistance proteins containing nucleotide-binding leucine-rich repeat domain that recognize viral effectors This model is similar to the defense mechanism of plants against other non-viral pathogens and it’s one of the main pathogen recognition systems in plants [4]. The newly grown leaves were healthy and immune to TRSV when they are infected by TRSV again [8] This effective mechanism for resisting viruses to restore symptoms and protecting plants from reinfection is RNAi. Small RNAs are the core of RNAi. Small RNAs from different sources can target to inactivate the invading virus and mediate the regulation of endogenous immune genes. Plants have highly diverse small RNAs-based regulatory pathways to meet the various functional requirements of their growth, metabolism and defense [9,13]
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