Abstract
During infection, Citrus tristeza virus (CTV) produces a non-coding subgenomic RNA referred to as low-molecular-weight tristeza 1 (LMT1), which for a long time has been considered as a by-product of the complex CTV replication machinery. In this study, we investigated the role of LMT1 in the virus infection cycle using a CTV variant that does not produce LMT1 (CTV-LMT1d). We showed that lack of LMT1 did not halt virus ability to replicate or form proper virions. However, the mutant virus demonstrated significantly reduced invasiveness and systemic spread in Nicotiana benthamiana as well as an inability to establish infection in citrus. Introduction of CTV-LMT1d into the herbaceous host resulted in elevation of the levels of salicylic acid (SA) and SA-responsive pathogenesis-related genes beyond those upon inoculation with wild-type (WT) virus (CTV-WT). Further analysis showed that the LMT1 RNA produced by CTV-WT or via ectopic expression in the N. benthamiana leaves suppressed SA accumulation and up-regulated an alternative oxidase gene, which appeared to mitigate the accumulation of reactive oxygen species. To the best of our knowledge, this is the first report of a plant viral long non-coding RNA being involved in counter-acting host response by subverting the SA-mediated plant defense.
Highlights
During host infection, viruses produce a vast number of different RNA species
To assess whether the introduced mutations affected production of low-molecular-weight tristeza 1 (LMT1) only, without a detrimental effect on other viral subgenomic RNAs (sgRNAs), we examined sgRNAs generated by Citrus tristeza virus (CTV)-WT and CTV-LMT1d using total RNA from the N. benthamiana leaves agroinfiltrated with pCTV-WT or pCTV-LMT1d construct (Figure 1B,C)
Our study examined the role of LMT1, a long ncRNAs (lncRNAs) of one of the largest RNA viruses in its
Summary
Viruses produce a vast number of different RNA species. Besides generating mRNAs for translation of their proteins, many viruses make non-coding RNAs (ncRNAs) [1,2,3].While functions of viral small ncRNAs such as small interfering RNAs (siRNAs) and microRNAs are relatively well understood, the roles of long ncRNAs (lncRNAs; RNAs over 150 nucleotides, nt) remain understudied. Besides generating mRNAs for translation of their proteins, many viruses make non-coding RNAs (ncRNAs) [1,2,3]. A number of those lncRNAs have been assigned various functions in the virus cycle favoring infection, including regulation of host and viral gene expression, virion production, and counteraction of the host antiviral response. Some of the best studied examples are lncRNAs produced by large double-stranded DNA viruses in the Adeno- and Herpesviridae families and non-coding subgenomic RNAs (sgRNAs) that are generated by positive-sense RNA viruses of the family Flaviviridae (reviewed in [2]). In addition to the lncRNAs of animal viruses, few lncRNAs were found in plant-infecting positive-sense RNA viruses belonging to the Luteo- and Tombusviridae families and in Cauliflower mosaic virus (CaMV), a pararetrovirus from the family Caulimoviridae
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