Genetic Analyses of the FRNK Motif Function of Turnip mosaic virus Uncover Multiple and Potentially Interactive Pathways of Cross-Protection

Abstract

Cross-protection triggered by a mild strain of virus acts as a prophylaxis to prevent subsequent infections by related viruses in plants; however, the underling mechanisms are not fully understood. Through mutagenesis, we isolated a mutant strain of Turnip mosaic virus (TuMV), named Tu-GK, that contains an Arg182Lys substitution in helper component-proteinase (HC-Pro(K)) that confers complete cross-protection against infection by a severe strain of TuMV in Nicotiana benthamiana, Arabidopsis thaliana Col-0, and the Arabidopsis dcl2-4/dcl4-1 double mutant defective in DICER-like ribonuclease (DCL)2/DCL4-mediated silencing. Our analyses showed that HC-Pro(K) loses the ability to interfere with microRNA pathways, although it retains a partial capability for RNA silencing suppression triggered by DCL. We further showed that Tu-GK infection triggers strong salicylic acid (SA)-dependent and SA-independent innate immunity responses. Our data suggest that DCL2/4-dependent and -independent RNA silencing pathways are involved, and may crosstalk with basal innate immunity pathways, in host defense and in cross-protection.

Tomato DCL2b is required for the biosynthesis of 22-nt small RNAs, the resulting secondary siRNAs, and the host defense against ToMV

“…2b). This result was consistent with previous studies in which the majority of vsiRNAs are 21-nt long in virus-infected plants 20,30,31 . Among the vsiRNAs, over 90% of the reads matched to ToMV, whereas 3.8% and 1.5% belonged to tomato mottle mosaic virus (ToMMV) and tomato brown rugose fruit virus (ToBRFV), respectively, with residue reads aligning to another 8000 viruses (Fig.…”

Development of a Mild Viral Expression System for Gain-Of-Function Study of Phytoplasma Effector In Planta

“…Because of silencing suppression, foreign proteins in viral vector-infected plants are expressed to a higher degree than in transgenic plants [16–18]. In addition, the viral suppressor interferes microRNA (miRNA) biogenesis, resulting in severe symptoms that affect the normal growth status of host plants [19, 20]. To overcome this issue, a deconstructed vector was applied for over-expression of a foreign gene through the expression of the required viral elements [21, 22].…”

“…HC-Pro R182K is a mutant of a gene-silencing suppressor that has lost its ability to suppress the miRNA pathway, results in no symptoms in TuGK-infected Arabidopsis thaliana (hereafter Arabidopsis) and Nicotiana benthamiana plants [19, 24]. TuGK has been modified as a viral vector to express GFP for indicating and monitoring the virus location in the host [19].…”

“…HC-Pro R182K is a mutant of a gene-silencing suppressor that has lost its ability to suppress the miRNA pathway, results in no symptoms in TuGK-infected Arabidopsis thaliana (hereafter Arabidopsis) and Nicotiana benthamiana plants [19, 24]. TuGK has been modified as a viral vector to express GFP for indicating and monitoring the virus location in the host [19]. An infectious, full-length cDNA clone of TuGK has been constructed in the mini binary vector pBD003 to generate pBD-TuGK, which can be directly inoculated into host plants via agro-infiltration to induce an initial infection [24].…”

“…An infectious, full-length cDNA clone of TuGK has been constructed in the mini binary vector pBD003 to generate pBD-TuGK, which can be directly inoculated into host plants via agro-infiltration to induce an initial infection [24]. TuGK-infected Arabidopsis plants is symptomless [19], making TuGK suitable for the over-expression of foreign genes in Arabidopsis plants, with few or no side effects due to the severe pathogenicity of the virus.…”