Food security is an issue of increasing concern as agricultural systems become highly intensified and yields near their forecasted ceiling. Viruses are present within agricultural systems at a much higher level than previously thought. Virus–plant interactions are obligate, symbiotic interactions that exist along a spectrum from parasitism to commensalism to mutualism. As viruses require a host’s molecular machinery to replicate, the host survival is important to an extent, and there is a trade-off between maximising replication or transmission (and host survival).
Low temperature is one of the major environmental factors limiting plant growth. Cold-sensitive plants are injured and stunted in growth when temperatures are well below those for normal growth but still above freezing. Virus infection changes expression of genes influencing cold tolerance (even under normal temperatures). Cucumber mosaic virus (CMV) has been shown to be mutualistic under cold conditions, with infected plants having greater survival (when compared to non-infected plants).
It may be possible to use an attenuated virus to induce mutualistic interactions increasing yield under cold conditions. This is particularly important as the amount of land capable of supporting agriculture is nearing its upper limit but use of plants carrying increased cold-resistance allow expansion into previously unused land. However, this is highly theoretical and requires further understanding on the mechanisms garnering mutualism under cold conditions.
In this project I tested the specificity of the mutualistic relationship between plant and virus formed under cold conditions by varying the plant species, virus and environment infection is occurring in. At present it is unknown whether the mutualism only occurs when CMV is present or if it is widespread within viruses.
In the experiment, I used both Cucumber mosaic virus and Turnip vein clearing virus in Arabidopsis thaliana. Throughout the experiment I monitored development of infected and mock-inoculated groups under different cold conditions. These cold conditions were ambient (20 degrees celsius), freezing (-4 degrees) and chilled (4 degrees).
Plants infected by viruses appeared to survive slightly better than the non-infected plants indicating the virus-host mutualism is non-specific to the virus-plant relationship but rather a relationship exhibited whenever infected plants are placed in cold environments. Similarly the level of infection was higher in the ambient temperature infected plants.
However, the results were not significant and there were experimental issues including the growth chamber used to house the plants being faulty throughout the experiment meaning the groups were not constantly kept at the correct temperature. This indicates that virus infected plants may be more resilient to temperature changes however further research is required.
I thoroughly enjoyed the experience provided to me by the BSPP vacation bursary and would highly recommend it to any student interested in plant pathology. During the course of the placement my interest in plant pathology increased as I delved further into the literature concerning my chosen topic. I was able to hone practical skills including inoculation of plants, extracting virus infected samples, growing/replanting Arabidopsis and testing the level of infectivity of the viruses in my samples using an ELISA. All of which were highly beneficial skills particularly as I had not used an ELISA prior to the internship and will be useful experience as I pursue a career in plant pathology.
Elias Saykouk
University of Bristol
