Molecular evolution of Pepino mosaic virus during long‐term passaging in different hosts and its impact on virus virulence

Abstract

In this study the effect of host changes and multiple passages on Pepino mosaic virus (PepMV) evolution was analysed. A population of a mild isolate of PepMV was used to generate five independent evolution lineages on three tomato cultivars, which differ in rate of appearance of symptoms and their severity during viral infection (Beta Lux, Moneymaker and Malinowy Ȯzarowski) and on Datura inoxia. Twenty serial passages were performed over a period of 217-220 days. Symptom severity was monitored along the entire experiment. After the last series of passages total RNAs from each lineage and host were isolated and the triple gene block 3 (TGB3) and coat protein (CP) were amplified, cloned and 10 clones for each gene sequenced. Among the 400 clones for both genes, 143 individual mutations (61 synonymous and 82 nonsynonymous) were identified, with the largest number of nonsynonymous mutations being observed for the tomato cultivars Malinowy Ȯzarowski and Beta Lux. In two of the lineages evolving in the most susceptible variety of tomato (Beta Lux) necrotic changes in leaf blades appeared after 17 passages, leading to death of the plants. In these two lineages the mutation responsible for necrotic symptoms was K67E in TGB3. The appearance of this convergent mutation in independently evolving lineages may suggest that selection in this experimental set up favours more aggressive PepMV variants. We found a positive association between the severity of symptoms and the amount of genetic variability contained on viral populations. Indeed, the severity of symptoms turned out to be a good predictor for several indices of molecular variability. In addition, mapping all observed mutations in CP and TGB3 protein structures revealed that most were located on the surface, indicating a possible implication in viral-viral or viral-host interactions.

Stable and Broad Spectrum Cross-Protection Against Pepino Mosaic Virus Attained by Mixed Infection

“…(iv) Nucleotide diversity values of passaged virus populations were low, and ranged from 0.0012 ± 0.0003 for PepMV-Sp13 and PS5 in single infections, to 0.0022 ± 0.0005 for PepMV-H30. A surprising aspect was the high ratio of non-synonymous to synonymous mutations, which ranged from 17/17 (1.0) for passaging of PepMV-Sp13 to 36/18 (2.0) for passaging of the same virus in mixed infection; we do not have an explanation for this phenomenon, but it is in agreement with previous reports on the experimental evolution of PepMV after passaging (Minicka et al, 2015). Interestingly, PepMV-Sp13 and PS5 passaged populations, either in single or in mixed infections, had lower nucleotide diversity values than those of the aggressive isolates PepMV-H30 or PepMV-KLP2.…”

Local adaptation of plant viruses: lessons from experimental evolution

“…Finally, in recent work, Minicka et al . () evolved a mild strain of pepino mosaic potexvirus (PepMV) into three S. lycopersicum cultivars that differed in their tolerance to infection with this virus over 20 passages, five independent lineages per tomato cultivar. Tolerance is a term that defines the property of a host to minimize virulence without necessarily affecting viral load (Little et al .…”

The transcriptomics of an experimentally evolved plant-virus interaction

“…Consequently, to better understand the evolution of viruses as obligate cellular parasites, it is essential to study them through a different perspective, focusing on where they thrive. Most evolution experiments performed with plant viruses to address the role of host diversity in the evolutionary fate of viral populations have focused in the use of different host species 9 10 11 12 13 14 15 16 17 18 19 . By contrast, very few studies have experimentally explored the role of within-host species diversity in resistance and susceptibility genes into the evolution of plant viral pathogens.…”