The games plant viruses play Santiago

2 Mixed virus infections in plants are common in nature. The outcome of such virus-virus interactions ranges from cooperation and coexistence (synergism) to mutual exclusion (antagonism). A priori, the outcome of mixed infections is hard to predict. To date, the analyses of plant virus mixed infections were limited to reports of emerging symptoms and/or to qualitative, at best quantitative, descriptions of the accumulation of both viruses. Here, we show that evolutionary game theory provides an adequate theoretical framework to analyze mixed viral infections and to predict the long-term evolution of the mixed populations. Highlihgts: • The outcome of mixed virus plant infections is complex and hard to predict • Game theory provides tools to study interactions between viruses • Mutual cooperation is the most commonly game played by plant viruses • Molecular biology of viruses may explain how certain games are played Introduction An interesting phenomenon of plant viral disease, which is not so common among animal viruses, is synergism during coinfection [1 ** ]. Coinfection by two distinct viruses or by two strains of the same virus results in complex interactions with unpredictable disease phenotypes [1 ** ]. In general, antagonistic interactions lead to mutual exclusion and, eventually, to cross-protection. By contrast, synergism enhances fitness components of at least one of the members of the viral complex and the effect on the host becomes greater than the sum of the individual effects. Mixed infections can also modify viral traits such as host range [2-5], transmission rate [6,7], cellular tropism [8,9], titer [3,10 * ,11], and even the biology and preference of vectors [12]. Umbraviruses and their luteovirus helpers provide particularly suggestive examples of synergism, illustrating the degree of dependence that can be achieved among pairs of viruses. Umbraviruses such as Groundnut rosette virus (GRV) do not encode for a coat protein and use the capsids of its luteovirus helper Groundnut rosette assistor virus (GRAV) for aphid transmission [13]. In this particular case, the situation is even more 3 complex since encapsidation of GRV in the GRAV capsid proteins requires of the intervention of a GRV satellite RNA that co-encapsidates [13]. In mixed infections, each viral population changes the environment and becomes part of the fitness landscape of the co-infecting virus population. Therefore, in mixed infections the success of any virus depends not only on its adaptation to the host, but also on how its behavior interacts with that of …