A Virus Which In Fact Helps The Host During Unsupportive Weather

Viruses always create a problem. This is a normal conception that we have. But proving this wrong, new research has found out that a virus actually has been seen benefitting its host in times of crisis.

The turnip mosaic virus (a virus which generally affects plants from the cabbage family), during periods of drought, can switch from damaging a plant to helping it by altering the host’s circadian clock so the plant loses less water.

The study conducted showed that when a species of wild weed, known as the thale cress (Arabidopsis thaliana), was infected with a particular variant of the virus, the plant was 25% more likely to survive the water stress.

All of this seemed to accord to the weather.

In normal conditions, the virus was acting as a pathogen killing watered plants.

Whereas in case of such a drought, the plants seem to stay alive, explains virologist Santiago Elena Fito, chairman of the Institute for Integrative Systems Biology (I2SysBio).

To find out the actual cause of these changes, the study was done by infecting healthy plants with variants of virus which had either evolved under drought-like conditions or had grown up under usual amounts of rainfall.

The plants were then either watered normally or subjected to water scarcity.

The virus which grew under normal conditions caused disease in plants, whereas the variants which developed in drought-like conditions showed more mercy, even when their hosts continued to be well watered.

This shows that drought-evolved viruses are somehow causing changes in the transcription of their host’s genes to help them better survive. Authors also found that the plants infected with these variants showed genetic changes linked to their circadian clock, which can influence a plant’s water use.

This knowledge could play an important role in places where more frequent and intense drought threatens the crops.

Previous studies show that some viruses can cause disease in cultivated plants, but not in wild plants. One thought on this is that the host-virus relationships fall on a spectrum from pathogenesis (or disease) to mutualism (where everybody benefits). And as shown, environmental conditions can have an important role in this.

Research in 2008 was seen to have several mosaic viruses that seemed to improve plant tolerance to environmental stress, boosting their antioxidants and water protection.

In 2013, another study showed drought and heat together could change the turnip mosaic virus’ signalling pathways, although this was thought to reduce the plant’s heat response and not improve it. 

This result is the first of its kind where environmental conditions can directly influence a virus’ relationship to its host, evolving from pathogenesis to mutualism in a single life cycle.

“We observed it before that a virus can confer drought tolerance to their host,” the authors write, “but, to our knowledge, this is the first time they explored how abiotic stresses shape the evolution of a host-virus interaction.

Some also suggest that when faced with a non-biological threat, some plants can adjust their metabolism, gene expression which can have an influence on the outcome of a viral infection.

The viruses growing under such drought-like conditions have learned not to destroy the host while it’s down.

The authors added that the data shows that virus adaptation to drought conditions results in a differential transcription change in their local hosts.

The viral infection can help the host survive and in turn ensure the survival of the virus itself. This is ultimately what allows the infection to replicate and spread even under stressful conditions.

Although the mechanism used by viruses to induce drought tolerance in plants is probably not universal, figuring out a way on how to turn these common infections from pathogens to partners, it could help us prepare our crops for the dry spells ahead.

Journal Reference:
Rubén González, Anamarija Butković, Francisco J. Escaray, Javier Martínez-Latorre, Ízan Melero, Enric Pérez-Parets, Aurelio Gómez-Cadenas, Pedro Carrasco, and Santiago F. Elena Plant virus evolution under strong drought conditions results in a transition from parasitism to mutualism PNAS February 9, 2021 118 (6) e2020990118; DOI: /10.1073/pnas.2020990118