Persistent Southern Tomato Virus (STV) Interacts with Cucumber Mosaic and/or Pepino Mosaic Virus in Mixed- Infections Modifying Plant Symptoms, Viral Titer and Small RNA Accumulation

Abstract

Southern tomato virus (STV) is a persistent virus that was, at the beginning, associated with some tomato fruit disorders. Subsequent studies showed that the virus did not induce apparent symptoms in single infections. Accordingly, the reported symptoms could be induced by the interaction of STV with other viruses, which frequently infect tomato. Here, we studied the effect of STV in co- and triple-infections with Cucumber mosaic virus (CMV) and Pepino mosaic virus (PepMV). Our results showed complex interactions among these viruses. Co-infections leaded to a synergism between STV and CMV or PepMV: STV increased CMV titer and plant symptoms at early infection stages, whereas PepMV only exacerbated the plant symptoms. CMV and PepMV co-infection showed an antagonistic interaction with a strong decrease of CMV titer and a modification of the plant symptoms with respect to the single infections. However, the presence of STV in a triple-infection abolished this antagonism, restoring the CMV titer and plant symptoms. The siRNAs analysis showed a total of 78 miRNAs, with 47 corresponding to novel miRNAs in tomato, which were expressed differentially in the plants that were infected with these viruses with respect to the control mock-inoculated plants. These miRNAs were involved in the regulation of important functions and their number and expression level varied, depending on the virus combination. The number of vsiRNAs in STV single-infected tomato plants was very small, but STV vsiRNAs increased with the presence of CMV and PepMV. Additionally, the rates of CMV and PepMV vsiRNAs varied depending on the virus combination. The frequencies of vsiRNAs in the viral genomes were not uniform, but they were not influenced by other viruses.

The Interplay between the Host Microbiome and Pathogenic Viral Infections

“…Axenic chickens infected with Marek’s disease virus had more severe disease ( 93 ). Similar enhancements can happen in plants, as plants persistently infected with Southern tomato virus develop stronger symptoms when infected with pathogenic viruses, such as cucumber mosaic and pepino mosaic viruses ( 94 ).…”

Discovery and Diagnosis of a New Sobemovirus Infecting Cyperus esculentus Showing Leaf Yellow Mosaic and Dwarfism Using Small-RNA High Throughput Sequencing

“…This suggests that XYDV could interfere with root development and plant growth in seedlings when XYCV concentration surpasses a certain threshold. A positive correlation between symptoms and viral accumulation has been also reported for several plant viruses [ 17 , 18 , 19 ], although this does not apply to tolerant hosts [ 20 ]. The correlation among XYDV accumulation and symptom manifestation, as well as the fact that XYDV was the only viral sequence found using HTS strongly supports that XYDV is the causal agent of the disease of leaf yellow mosaic and dwarfism in C. esculentus .…”

Detection of Persistent Viruses by High-Throughput Sequencing in Tomato and Pepper from Panama: Phylogenetic and Evolutionary Studies

“…The biological role of p42 remains unclear; it has been suggested that it is the STV capsid protein, but virions have been never observed and no homologies with other viral capsid proteins have been found [6]. Moreover, recent studies showed that p42 has no RNA silencing suppressor activity [4]. Differences in the purifying selection pressure in both p42 overlapping and non-overlapping regions found in RdRp, with stronger pressure in the first one, reinforce the hypothesis of the in vivo expression of p42-although its biological function remains unknown.…”

“…Some of them, such as the white clover cryptic virus 1 (WCCV-1) and curvularia thermal tolerance virus (CThTV), establish symbiotic relationships with their hosts [2,3]. Nevertheless, recent studies have shown that southern tomato virus (STV), a persistent virus infecting tomato (Solanum lycopersicum), interacts with cucumber mosaic virus (CMV) and pepino mosaic virus (PepMV) in mixed infections by increasing the pathogenic effect of these viruses [4]. Besides this, the presence of STV-induced changes with the accumulation of some regulatory micro-RNAs (miRNAs) that target plant genes involved in essential plant processes such as plant development and responses to biotic or abiotic stress [4,5].…”