Salicylic acid treatment and expression of an RNA-dependent RNA polymerase 1 transgene inhibit lethal symptoms and meristem invasion during tobacco mosaic virus infection in Nicotiana benthamiana

Abstract

BackgroundHost RNA-dependent RNA polymerases (RDRs) 1 and 6 contribute to antiviral RNA silencing in plants. RDR6 is constitutively expressed and was previously shown to limit invasion of Nicotiana benthamiana meristem tissue by potato virus X and thereby inhibit disease development. RDR1 is inducible by salicylic acid (SA) and several other phytohormones. But although it contributes to basal resistance to tobacco mosaic virus (TMV) it is dispensable for SA-induced resistance in inoculated leaves. The laboratory accession of N. benthamiana is a natural rdr1 mutant and highly susceptible to TMV. However, TMV-induced symptoms are ameliorated in transgenic plants expressing Medicago truncatula RDR1.ResultsIn MtRDR1-transgenic N. benthamiana plants the spread of TMV expressing the green fluorescent protein (TMV.GFP) into upper, non-inoculated, leaves was not inhibited. However, in these plants exclusion of TMV.GFP from the apical meristem and adjacent stem tissue was greater than in control plants and this exclusion effect was enhanced by SA. TMV normally kills N. benthamiana plants but although MtRDR1-transgenic plants initially displayed virus-induced necrosis they subsequently recovered. Recovery from disease was markedly enhanced by SA treatment in MtRDR1-transgenic plants whereas in control plants SA delayed but did not prevent systemic necrosis and death. Following SA treatment of MtRDR1-transgenic plants, extractable RDR enzyme activity was increased and Western blot analysis of RDR extracts revealed a band cross-reacting with an antibody raised against MtRDR1. Expression of MtRDR1 in the transgenic N. benthamiana plants was driven by a constitutive 35S promoter derived from cauliflower mosaic virus, confirmed to be non-responsive to SA. This suggests that the effects of SA on MtRDR1 are exerted at a post-transcriptional level.ConclusionsMtRDR1 inhibits severe symptom development by limiting spread of virus into the growing tips of infected plants. Thus, RDR1 may act in a similar fashion to RDR6. MtRDR1 and SA acted additively to further promote recovery from disease symptoms in MtRDR1-transgenic plants. Thus it is possible that SA promotes MtRDR1 activity and/or stability through post-transcriptional effects.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0705-8) contains supplementary material, which is available to authorized users.

Modulation of host plant immunity by Tobamovirus proteins

“…Moreover, it was shown that transgenic NtRDR1 antisense tobacco plants are more susceptible to TMV infection than wild-type plants (Xie et al, 2001). There are many reports demonstrating the role played by RDR1 and RDR6 in the defence against viruses (Pandey and Baldwin, 2007;Liu et al, 2009;Rakhshandehroo et al, 2009;Qin et al, 2012;Liao et al, 2014;Lee et al, 2016). Thus, there are several reports which support the RDR1 contribution to the antiviral defence mechanism during Tobamovirus infections.…”

“…Orthologous genes of NtRDR1 have also been characterized in other species, such as Nicotiana glutinosa (NgRDR1), Nicotiana benthamiana (NbRDR1m), A. thaliana (AtRDR1), Medicago truncatula (MtRDR1) and rice (OsRDR1), all of them being induced by both viral infection and SA treatment (Yu et al, 2003;Yang et al, 2004;Quilis et al, 2008;Liu et al, 2009). Several findings indicate that RDR1 could be involved in the SA-induced resistance against viruses (Alamillo et al, 2006;Lee et al, 2016). The impact of SA on the modulation of RDR1 action was demonstrated in tobacco NahG transgenic plants infected with PPV.…”

“…These plants accumulated lower levels of vsiRNAs than wild-type tobacco, and this reduced accumulation is associated with the pattern of expression of RDR1 (Alamillo et al, 2006). The involvement of RDR1 in antiviral SA-mediated resistance was also explored in transgenic N. benthamiana plants constitutively expressing MtRDR1 (Lee et al, 2016). MtRDR1 expression did not restrict TMV movement into non-inoculated tissues, but its expression was able to inhibit the extent of spread of TMV into the tissues adjacent to the apical meristem.…”

Recent Biotechnological Advances in the Improvement of Cassava

“…Mechanistically, non-host resistance is likely due to an intrinsic lack of susceptibility, which is a multigenic trait. It is now known that natural compounds, such as melatonin that modulate immune responses, such as ROS metabolism, calcium signaling and mitogen-activated protein kinase (MAPK) cascades, can be used to enhance natural resistance [106]. Notably, the recent identification and functional analysis of melatonin synthesis genes in cassava has provided a direct link between melatonin and immune responses [107].…”

Bensulfuron-Methyl Treatment of Soil Affects the Infestation of Whitefly, Aphid, and Tobacco Mosaic Virus on Nicotiana tabacum

“…In the interaction between viruses and phytohormones, RNA-dependent RNA polymerase ( RDR ) family is involved in the establishing of the resistance in host plants. In MtRDR1 transgenic tobaccos, MtRDR1 can function as RDR6 and can help the host plants to recover from the symptom caused by virus infection in the presence of SA (Lee et al, 2016). …”