Using Game Theory to Understand Systemic Acquired Resistance as a Bet-Hedging Option for Increasing Fitness When Disease Is Uncertain.

Gregory J Reynolds,Thomas R Gordon,Neil Mcroberts

doi:10.3390/plants8070219

Gregory J Reynolds, Thomas R Gordon + Show 1 more

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https://doi.org/10.3390/plants8070219

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Abstract

Systemic acquired resistance (SAR) is a mechanism through which plants may respond to initial challenge by a pathogen through activation of inducible defense responses, thereby increasing resistance to subsequent infection attempts. Fitness costs are assumed to be incurred by plants induced for SAR, and several studies have attempted to quantify these costs. We developed a mathematical model, motivated by game-theoretic concepts, to simulate competition between hypothetical plant populations with and without SAR to examine conditions under which the phenomenon of SAR may have evolved. Data were gathered from various studies on fitness costs of induced resistance on life history traits in different plant hosts and scaled as a proportion of the values in control cohorts in each study (i.e., healthy plants unprimed for SAR). With unprimed healthy control plants set to a fitness value of 1, primed healthy plants incurred a fitness cost of about 10.4% (0.896, n = 157), primed diseased plants incurred a fitness cost of about 15.5% (0.845, n = 54), and unprimed diseased plants incurred a fitness cost of about 28.9% (0.711, n = 69). Starting from a small proportion of the population (0.5%) and competing against a population with constitutive defenses alone in stochastic simulations, the SAR phenotype almost always dominated the population after 1000 generations when the probability of disease was greater than or equal to 0.5 regardless of the probability for priming errors.

Highlights

Over the course of their evolution, plants have developed defenses to reduce damage by pathogens.In addition to constitutive defenses, such as cell walls or bark, plants may resist attack by these parasites with inducible defenses
Systemic acquired resistance (SAR) is a mechanism by which plants may respond to an initial pathogen or microbe challenge by activating some of these inducible defense responses, thereby increasing resistance to subsequent infections [1]
Compiled studies focused on a range of plant hosts and inducers of resistance, including Monterey pine induced by Fusarium circinatum [26], wheat (Triticum aestivum L.) induced chemically [27], tobacco (Nicotiana tabacum L.) induced by Peronospora hyoscyami (Rabenh.) de Bary [28], barley (Hordeum vulgare L.) induced chemically [29] and by an avirulent

Summary

Introduction

Over the course of their evolution, plants have developed defenses to reduce damage by pathogens. In addition to constitutive defenses, such as cell walls or bark, plants may resist attack by these parasites with inducible defenses. Systemic acquired resistance (SAR) is a mechanism by which plants may respond to an initial pathogen or microbe challenge by activating some of these inducible defense responses, thereby increasing resistance to subsequent infections [1]. The term “priming” is used to refer to the set of molecular, biochemical, and physiological changes that occur in a plant when an environmental cue indicates an increased probability of pathogen attack. It is important to note the distinction between priming of active resistance mechanisms and active resistance itself.

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