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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
 

Lead Supervisor:  John Carr, Plant Sciences

Co-Supervisors: Alex Murphy, Plant Sciences and Trisna Tungadi, Plant Sciences

Importance of the area of research concerned: 
Most research on viruses focuses on disease but an increasing body of evidence suggest that under some conditions viruses of animals and plants act as mutualists (Roossinck & Bazán, 2017). For example, many plant viruses render their hosts resistant to drought (Carr, 2017) and a virus has been shown to make infected plants more attractive to bumblebee pollinators (Groen et al., 2016). It has been suggested that these phenomena will favour reproduction of virus‐susceptible plants over that of resistant or uninfected plants; increasing inheritance of genes for susceptibility, and inhibiting inheritance of resistance. Mathematical modelling appears to support this and raises the possibility that viruses could influence plant evolution by decreasing the selective advantage of genes for resistance (Groen et al., 2016). Indeed, it is becoming more widely accepted that plant viruses can affect the evolution of their hosts (Carr, 2017; Roossinck & Bazán, 2017). The key objective is to experimentally test this ‘payback’ hypothesis using drought conditions over multiple generations to see virus-infected susceptible plants reproduce more successfully than resistant plants.
Project summary : 
It seems increasingly likely that in wild plant communities viruses act as mutualists and may drive plant evolution. Although viruses are important disease agents, could it be that sometimes viruses help their hosts? A popular model, the ‘arms-race’ theory, proposes that evolution of resistance forces more aggressive virus strains to evolve, which in turn drive evolution of better-defended plants and so on, ad infinitum. We think this oversimplifies plant-virus interactions since ‘deal-making’ also occurs. For example, many viruses ‘pay back’ plants by improving drought survival. Hypothetically, resistance becomes a liability if only virus-infected plants survive drought. We will: 1. Use multi-generation ‘artificial evolution’ experiments to investigate the competitiveness of susceptible versus resistant plants under drought, and 2. Determine how virus-induced drought survival works.
What will the student do?: 
The weed arabidopsis has a rapid 8-week generation time is ideal for ‘artificial evolution’ studies. One of its most important viruses is turnip mosaic virus, which enhances drought resilience in infected plants. Depriving Arabidopsis of water for 14d (before re-irrigation to allow flowering/seed-set) decreases plant survival to <10%, with survivors yielding 20% of control seed numbers. Starting with 1000 seed (susceptible:resistant in various proportions), selection scenarios will be imposed. Under Scenario 1 (no drought, all plants infected) the ‘arms-race’ hypothesis should hold with virus-induced decreases in seed yield, causing a 9:1 susceptible:resistant starting population to be 99% resistant in 5 generations (Cf. Control Scenario 2, no virus/no drought: ratios will not change). Under Scenario 3 imposing drought conditions in addition to viral challenge will depress virus-resistant plant seed yield by 80%. If the payback hypothesis is correct, a 9:1 resistant:susceptible population will become >98% susceptible in 6 generations. We will also investigate production of compatible solutes & phytohormones in infected plants to understand the mechanisms of drought resilience.
References: 
Carr, J.P. 2017. Exploring how viruses enhance plants' resilience to drought and the limits to this form of viral payback. Plant, Cell and Environment, vol. 40(12) pp. 2906-2908., DOI: 10.1111/pce.13068
Groen, S.C., et al. 2016. Virus infection of plants alters pollinator preference: A payback for susceptible hosts? PLoS Pathogens, vol. 12(8), article number e1005790., doi:10.1371/journal.ppat.1005790
Roossinck, M.J., & Bazán, E.R. 2017. Symbiosis: Viruses as intimate partners. Annual Review of Virology, vol. 4, pp. 123-139., doi.org/10.1146/annurev-virology-110615-042323
Applying
You can find out about applying for this project on the Department of Plant Sciences page.