Differential contributions of plant Dicer‐like proteins to antiviral defences against potato virus X in leaves and roots

Abstract

SUMMARYMembers of the plant Dicer-like (DCL) protein family are the critical components of the RNA-silencing pathway that mediates innate antiviral defence. The distinct antiviral role of each individual DCL protein has been established with mostly based on observations of aerial parts of plants. Thus, although the roots are closely associated with the life cycle of many plant viruses, little is known about the antiviral activities of DCL proteins in roots. We observed that antiviral silencing strongly inhibits potato virus X (PVX) replication in roots of some susceptible Solanaceae species. Silencing of the DCL4 homolog in Nicotiana benthamiana partially elevated PVX replication levels in roots. In Arabidopsis thaliana, which was originally considered a non-host plant of PVX, high levels of PVX accumulation in inoculated leaves were achieved by inactivation of DCL4, while in the upper leaves and roots, it required the additional inactivation of DCL2. In transgenic A. thaliana carrying the PVX amplicon with a green fluorescent protein (GFP) gene insertion in the chromosome (AMP243 line), absence of DCL4 enabled high levels of PVX-GFP accumulation in various aerial organs but not in the roots, suggesting that DCL4 is critical for intracellular antiviral silencing in shoots but not in roots, where it can be functionally compensated by other DCL proteins. Together, the high level of functional redundancies among DCL proteins may contribute to the potent antiviral activities against PVX replication in roots.

Functional and Genetic Analysis Identify a Role for Arabidopsis ARGONAUTE5 in Antiviral RNA Silencing

“…This result suggests that both DCL2 and DCL4 are required in local and systemic leaves to restrict PVX although DCL2 appear to be less important in local leaves. Our results are similar to a recent report showing that the dcl2 dcl4 mutant is susceptible to PVX, although they did not find that dcl2 and dcl4 single mutants were systemically susceptible to PVX (Andika et al, 2015). This may be due to inoculation method or dosage as DCL2 activity may be overcome by increasing inoculum (Deleris et al, 2006) or different growth conditions, which can alter RNA silencing efficiency (Zhang et al, 2012;Ma et al, 2015).…”

“…Although the PVX VSR, P25, destabilizes Arabidopsis AGO1, this virus does not normally systemically infect Arabidopsis Columbia-0 (Col-0) (Chiu et al, 2010;Jaubert et al, 2011). However, PVX can effectively infect Arabidopsis if a VSR is supplied in trans from a second virus or if RNA silencing is attenuated by mutation of DCL-encoding genes or AGO2 Andika et al, 2015). At the same time, PVX accumulates to a lesser extent in the ago2 mutant than it does in a triple dicer (dcl2 dcl3 dcl4) mutant , suggesting that at least one other AGO protein may function in resistance to PVX in Arabidopsis in concert with AGO2.…”

High-Throughput Sequencing and the Viromic Study of Grapevine Leaves: From the Detection of Grapevine-Infecting Viruses to the Description of a New Environmental Tymovirales Member

“…Nicotiana benthamiana [wild-type, NbDCLx mutant (Andika et al, 2015) and transgenic B2 (Monsion et al, 2018)] and Chenopodium quinoa were grown in growth chambers kept at 22/18°C (day/night) with a 14/10 h light/dark photoperiod. Similar settings were also used for the mechanical transmission experiments.…”

Roles of Dicer-Like Proteins 2 and 4 in Intra- and Intercellular Antiviral Silencing

“…For instance, DCL4 and DCL4-processed 21-nucleotide vsiRNAs are involved in virusinduced RNA silencing (also known as VIGS), a kind of posttranscriptional gene silencing (PTGS; Bouché et al, 2006;Garcia-Ruiz et al, 2010;Qu et al, 2008). DCL2 and its cognate 22-nucleotide vsiRNAs may also affect VIGS in plant cells when DCL4 is absent or defective (Andika et al, 2015;Wang et al, 2011;Zhang et al, 2012). On the other hand, DCL3 and 24-nucleotide vsiRNAs are associated with RdDM and transcriptional gene silencing (TGS) in the protection of plant cells from DNA virus infection (Aregger et al, 2012;Blevins et al, 2006).…”